The 3E monk was the weakest class in the players handbook, and its not even a very close margin. Building an effective monk was literally impossible. .
I guess it depends on what you define as weak. And what you define as effective.
I've played a bunch of monks and they are almost always the most effective member of the party, or at least top half regardless of group.
Are they a fighter? No. Do they replace the fighter? Usually no.
Are they a rogue? No. Do they avoid obstacles like a rogue? Yes.
Are they a wizard? No. Are they as squishy? No. Do they perform extraordinary fears? Yes.
It all depends on what you are looking for from the class. I've tried to appeal to the ascetics of the monk but we have clearly moved onto abilities so I'll discuss that.
What do all those resistances, avoidance and "cute" bonuses amount to? Well together they create a class that can live through most any encounter. They aren't a fighter and it is has been a real problem to try and fix people of that view.
If you take a fighter and make him a monk then he'll be a poor monk. The same goes the other way.
While they need a certain amount of 'martial artist' and combat effectiveness they don't need to be the only ones who do so. They also significantly need the "cute" extras that are typically restricted to rogues. That is something you aren't going to get by just making a rogue or a fighter, you need aspects of BOTH to make a good monk.
3.) Hard to capitalize on or integrate into a team game
You bring up "team"-ness later as well but I'll cover it here.
Who says DnD IS a team game?
Who says it HAS TO BE one?
Who says DnD can only be one?
Who says you can't run non-team oriented games?
The (correct) answer to all of those is NO ONE. That makes your comments about DnD being a team game very irrelevant. Especially since we can't (as a community) seem to agree if DnD is or should be a team game.
That is just a minor nit-pick that has nothing to do with your overall comments about monk.
1.) Everyone can heal themselves with Hit Dice in 5E and as a Fighter the Martial Artist is the best at it.
2.) Mid-combat healing is more restricted in 5E.
3.) 4E Fighters could already self-heal with powers.
4.) The Martial Arist Combat Superiority tree could easily include an option to use Hit Dice mid-combat.
Everyone in 4e and 5e (so far) can heal themselves. But the thing that you (and apparently WotC) are ignoring is IF THEY ALL SHOULD. I'm firmly in the camp that they shouldn't.
As healing (both natural and supernatural) are highly contested debates I would suggest that perhaps you need to find another and more convincing argument against that aspect of the monk.
3.) Cuts into the Elven racial ability - terrible for a class that should be open for everyone, OK for a specialty.
2.) Cuts into the Dwarven racial ability - terrible for a class that should be open for everyone, OK for a specialty.
Wait... when a class cuts into racial features that is bad? When it DOESN'T cut into class features that is good?
Put another way.
X shouldn't be allowed because elves/dwarves get that.
Y shouldn't just be a monk feature, it should be a fighter/rogue.
I'm sensing some inconsistencies. It is like saying monks are bad because they grant darkvision/low-light and no one should ever get that except from their race. Oh but if monks DO have that then they should have to share it with any other class too.
It all just illustrates how big a train-wreck the AD&D / 3E monk class was.
We get it, 3e = bad, 4e = good.
AD&D/3E Monk - he knows Kung Fu and he's still one of the last guys to get picked for the dodge-ball team.
Unless the purpose of dodgeball changed since I was a kid, you would DEFINITELY want the guy who can't get hit and is immune from being kicked from the game or otherwise removed from your team. Those exception abilities and immunities make monks like the best dodgeball players ever. Plus, every monk I've ever played can't be hit or killed so..
I would prefer the monk be a background. You want to be a monk who excels at martial skill? Fighter with the monk background. You want to be a monk who flips out, runs up walls, and blends into the shadows? Rogue with the monk background. You want a monk with supernatural abilities? Wizard/Sorcerer/Warlock with the monk background.
First, a fighter with the monk background I get.. ish.
Second, a rogue with the monk background I get.. ish
Third, a wizard with the monk background.. I don't get.
Fourth, you didn't even try to say cleric with the monk background... and monks are SUPPOSED to be clerics so...
Fifth, all the backgrounds we have seen so far are relatively minor. They grant a couple +3's to certain skill checks. So how do you replace an entire class with those?
Sixth, what happens if you (as they have already expressed) don't want to use backgrounds and yet still want to play a monk?
Seventh, what do you have to give up in order to be a monk with this system? This is of course assuming you solve the 5th question's problem of actually using backgrounds to create monk abilities.
Because assuming you use something other than backgrounds to create a monk, such as specialties/traits/whatever they're calling them now, you won't be able to be an archer anymore because all of your specs/traits are now ALL monk.
Eighth, monk abilities can't be easily summed up in a small background. They aren't like "growing up poor; get a +3 on all poor-related checks". They are like "spend whole life training your mind and body (and soul?) to be better than you would have been otherwise; gain J,K,L,X,Y,Z,A,B,C,D abilities". Note, abilities =/= not skill checks.