Hiya!
I'm just gonna pop my head in here for a quick depositing of my 2¢.

[MENTION=6880599]ClaytonCross[/MENTION] : I think what's going on is most definitely a matter of DM and Player "style" or "preferred play". In the closest post above this, you wrote:
"
The more I have played as GM and a player at the same time the more I see GMs saying these things and realize a lot of hate for "balance" from both sides is because the GM just don't want to take the time to look at their player characters and build for them to make it harder with the same CR battles and/or ensure they are not telling a story by themselves instead of playing a game together. Putting a trap in front of your players that they lack the skill to even possibly meat or exceed in order to even detect it is not "independent world building" it is railroading players and story telling how a player(s) died to a trap. Again ... That is my opinion, anyway."
That right there. I think that is the schism you and some other posters on here are getting hung up on. What that paragraph says, to me, is "a DM needs to make stuff fair for the PC's". The PROBLEM comes when we look at the word "fair".
To you, [MENTION=6880599]ClaytonCross[/MENTION], "fair" means "challenges the PC's have a chance of overcoming based on their numbers/abilities/mechanics". A DC 20 trap that half the PC's can make on a 14+ will seem "fair". A situation where being able to speak Kuo-Toa ("aquatic" I guess) will seem "fair" if at least one or two PC's in the group can speak it. But the same thing, DC20 and speaking Aquatic, where none of the PC's can do it at all, or would need to roll 18+, would seem "unfair" to you.
To me (and some others?), "fair" means "all things considered in campaign world terms, a level playing field for anyone, pursuant to the 'life choices' the PC or NPC made while growing up in said campaign world". This you mentioned in your second paragraph, about how a DM just makes stuff "independent of the PC's". In particular "
I don't change my fights when a player doesn't make a session or if they rolled it as a random encounter, its on the players to deal with what ever comes at them", "My challenges are hard in fact I don't know if if any of my players could even meet the DCs with a 20 unless I allow critical success on skill tests, but hay its just the world we agreed to as a group. If this DC is just a little higher than the traps they beat last session with a 19 that is just the way it is". This, to many DM's (and players!) of a more "old skool" bent (ones like me who learned DM'ing back in 1981, +/- a year or two) this is the very
definition of what a "fair" campaign is like.
When a player encounters a raging river and his character needs to make a DC 16 Athletics test to cross without drowning...and then, 3 months later with all new PC's, the player encounters that same raging river and his new character needs to make a DC 20 Athletics test to cross without drowning. Well, that is not "fair". What this does is the exact opposite, IMNSHO, of what you are claiming it does. You claim it takes away player agency when a PC can't succeed (or has very little chance) when a DM has a DC 20 test for Situation A...regardless of the PC's capabilities and skills. I would submit that by changing what skills are needed for something, or what DC some task is, or what ability/spell can overcome it, based on the players characters,
that takes away player agency. It does that because it seems to not matter what the player chooses for his PC; because the DM will never put that PC in an "unwinable" situation. In short, the player and his PC's chance of success is based on what the DM feels it should be...not on what the player chose for his PC.
All in all, the bottom line is simple: You and your players definition of "fair" and what me (and some others) is are more or less diametrically opposed. Neither is "the right way". Both are "the right way"...but for different groups.
PS: Yes, I'm what you...and others...and even myself...could be termed a "killer DM". I have MOUNDS of dead PC's at my feet...probably well over a thousand (been DM'ing since '81). And that's just counting D&D (all editions)! Add in other games and, well, yeah...I'd probably be brought up on crimes against humanity/demihumanity/nonhumanity in a second!

My players? Yes. I typically have players stay with me for decades. I have two players who've been with me for about 2 decades now. My late wife was with me for almost 3 decades. One player who just moved down south was with me for just over 3 decades. Many other players have played for years at a time over the span of 3 decades. So I must be doing something right.
PPS: I also have a handful of my players PC's who are, bar none, HEROES and HEROINES in every sense of the word. They are mid to high level (6th to high teens...even three that hit 20th, 20th, and 22nd), over the nigh-on 4 decades I've been at this RPG thing. The players WORKED for those levels! They
survived by clever play, dogged determination, and excellent group cooperation. They've downed the Slavers, taken out a demi-god on her home plane, saved entire countries from threats from beneath the earth, removed demon worshipers from the highest levels of government who were bent on sacrificing the entire population, and a myriad of other epic successes. So when we see "Elminster", "Drizz't", and many other FR (the biggest offender) so-called 'heroes'...we chuckle. They're cute and all, but they were created that way and had their 'stories' pre-planned and rigged in their favour. At least many (all?) of the high level major NPC's in Greyhawk were all PC's in Gary's campaign and THEY survived. And all of my players PC's? FAR more impressive when you know what they had to go through to get there! (re: surviving in a supposedly "unfair" world run by a killer DM...

Sorry...couldn't resist!).
^_^
Paul L. Ming