So I had the misfortune recently of playing a Level 0 Character Funnel for my first experience of Dungeon Crawl Classics.
The experience has completely soured me on the game system.
First off, I guess you can't win them all. Better luck in your next campaign!
Secondly, don't claim something is bad just because you had a bad experience.
It's important to realize WHY the funnel is used.
What is is intended to accomplish?
Some players have a "charbuild" approach to gaming. The focus isn't so much on characterizing a living breathing person with his or her flaws and strengths, but to use the character as the tool to influence the world. By "influencing" I mean things like: accomplishing goals, defeating monsters, successfully completing scenarios.
The character in itself isn't so important just as long as it can do its job. The focus can often be on dealing a lot of damage or being very hard to impact with spells. Numbers. Statistics. Minmaxing.
In this regard, the character is just the vessel the player is steering in order to achieve goals. Furthermore, many D&D players expect and assume nobody will take this character away, except possibly at first level. But many spend a lot of time planning out the first ten levels or all twenty levels already before the first session.
The bulk of "characterization" becomes: choosing the best class abilities, looking for the best equipment and so on. The notion that this character is a real person with actual insecurities or weaknesses is remote or non-existent.
In my view, the funnel is designed to challenge this view, and bring such gamers out of their comfort zone.
The funnel accomplishes several things:
You aren't entitled to an awesome high-level character. You need to work to deserve one.
In far too much D&D scenarios the text and the NPC tells you you are a great hero, regardless of whether you have actually worked to deserve that. D&D fosters a mentality where you basically become a great hero just by showing up to play.
This is the mentality DCC aims to challenge with the funnel concept.
Instead of you automatically becoming a hero, you actually need to work to become one, by doing actual heroics. What defines a hero? Well, it's taking the dangerous route even when a safer exit presents itself because it's the right thing to do. But D&D combat mechanisms ensure that just showing up for combat isn't heroic. Combat in D&D is a reward, not something lesser men avoids.
By asking you to do dangerous adventures where there is a real risk of death and defeat you foster an atmosphere of actually growing into being a hero.
And as this hero you will remember your fallen friends and acquaintances. Because there will be some of those. You will yourself carry the sting of seeing your characters die, sometimes even when they did everything right.
This makes for a far richer campaign start than regular D&D, where you are almost assured of living to become a great hero already when you sign up at level 1.
I would say a DCC hero is much more deserving of the "hero" epithet than a D&D one, simply because you the player have yourself experienced how choosing the heroic and dangerous choice can and will lead to death, and skill and luck have created and formed you and you are a survivor, carrying actual scars.
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So. That's the background and rationale of the funnel system.
Now it's important to note that lots of gamers already play rpgs in such a way where developing an actual personality for their characters is an important aspect. And in these cases it's 100% okay to skip the funnel.
You see? The funnel is a tool you should use to shake D&D rollplayers out of their focus on numbers and minmaxing, and hopefully start thinking about their character's hopes and dreams, their character's fears and failures!
Now to your three objections:
1) Six players. Four characters each. Two actions a turn. For a ridiculous 48 actions per turn (plus the monsters actions.) Keeping up with positioning of 24 characters, what they're doing, etc.
1) A good GM uses very quick and fluid rules for the first few sessions, before the character roster has been whittled down. For instance, don't place each character individually on the map. Just ask the player "do Bob lead the group, does he hang back, or is he in the middle". This should result in the gang of characters being led by 6 brave characters, and if there is an ambush from behind, the GM knows which six characters are cowards or volunteers for the rear guard.
Then don't track exactly who is fighting who. The first round, the first (or last) line of six characters engage with monsters. Then, on subsequent rounds, each player makes six attack rolls. You can roll damage, but I would simply say rolling high kills the monster and rolling low don't.
There is no reason to go into details over how a single character spends its action allowance. Focus on speed and resolving the combat, so the players get to role-play their joy of surviving and/or lament the loss of the fallen.
A level 1 DCC character is exceedingly simple with very few mechanical details.
As the funnel whittles down the number of characters to 1 per player (or 2 per player tops) you can start engaging with the full combat system.
Sounds like your GM wasn't prepared for DCC and attempted to run the combat in the same way you would do for 5 heroes...
2) Random character creation is awful in the system, because your class/background has no bearing on your ability scores. So I had an elven sage with a 4 Int. Even if he survived, what would I have wanted to do, play a worthless elf who couldn't even use magic.
Old school baby! The notion here is that the player that manages to have his character survive despite a debilitating handicap is rewarded with a higher satisfaction. There's no notion of "the game should ensure fairness". Life isn't fair like that. If Bob rolls only 18s the solution is simple:
have him go first all the time!
Compare a game of Lord of the Rings. A Hobbit is not meant to be given equal opportunities as an Elf or Dwarf. The group should have the mindset that overcoming challenges together is what counts, even if the Elf needs to carry a greater burden during combat encounters (killing more Orcs) than the Halfling.
Same here: there are no (okay, almost no) unplayable characters. Even the hero with low scores could get a moment to shine!
Plus: the funnel gives you four characters! Chances are, at least one of them will be somewhat playable. So enjoy your Elf Wizard for as long as you want.

If he survives, perhaps you've grown attached and keep playing him despite his handicap. Or you let him retire in peace, satisfied you helped him avoid death.
You can always roll up more characters later. Yes you only start with 4 but only the most dogmatic of GMs would insist you stick with them if you don't fancy any one them.
In fact, many DCC adventures make a point of telling the GM which NPCs would be suitable to be "adopted" by a player short on characters. Let's take an example: the adventure has you fight cannibal cave men. Pure happenstance means that one of these survives a combat encounter, and now your group debates what to do with her.
But let's say you lost your fourth and final character in that fight. If you declare the cave NPC is a woman named "Gabi" and you want to play her, the GM can easily agree. You roll up stats as normal for this 5th character (it's best not to reuse her "monster stats") except you already know her equipment and her profession.
The randomness is - again - intended to tell players to not focus so much on numbers, and instead try to bring a real personality to life. DCC only uses +3 to -3 for a reason. The modifiers doesn't matter as much as in 3E or 5E.
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More importantly (and you probably couldn't have known, unless your GM had the foresight to tell you):
ability scores are much more fluid in DCC.
Or, at least, they can be. Or, if you ask me, they should be!
That is, it is much MUCH less of a big deal if you don't start with a 16 in Strength as a Fighter. Maybe you will find a sorcerous potion later which grants you extra Strength points. Maybe you fall into a random trap and get lucky. Maybe you'll even sell your soul to a Demon or Necromancer in exchange for higher Strength!
Quest for it! is the answer to every problem in DCC!
3) Random die rolls to kill characters. If you're going to use a character funnel with a stable of characters, the player should be able to volunteer the character to be killed as "tribute" - or at least have their actions lead to the character death. My best characters died before I got a chance to make a single decision and I was left with garbage tier random generated losers unfit to adventure.
Why?
Why should the player have control, when the whole point of being a hero is that you weren't given a promise you would become one? You just did the right thing and ended up victorious.
The key thing is: in order for putting your life on the line to be heroic, your life really needs to be put on the line.
Regular D&D is so very heavily slanted towards PC survival that this - in the eyes of OSR and DCC - does not count as actual heroism.
Only when you see your friends and comrades fall beside you, getting killed or maimed or transformed or worse, does your willingness for sacrifice carry real weight.
The idea here is that each time your lucky PC gets killed by a random event, the rest of the group gets a galvanizing event to carry with them.
And when you finally manage to roll up a character with high scores AND see him live beyond the first few levels (where death happens most often) it will be a real accomplishment and something to truly cherish.
This is a completely different mindset to ordinary D&D - where you expect that in return for showing up you will be next to guaranteed a good time, and a capable hero. Neither mindset is wrong. Point here is that declaring the DCC funnel as "bad" only betrays you don't realize what its aims are.
Had you known why DCC uses the funnel, you could have said "DCC funnel is not for me" and that would be fair. That's different from claiming the concept is bad, is what I'm saying.