As people would often point out in the 3.5 era, most of the most broken things in the system were in the PHB. Casting in Wild Shape for Druids. Animal Companions that seemed about as powerful as other PC's. Sno Cone Wish Machine shenanigans with Simulacrum for Wizards. Cleric's using Righteous Might ahd Divine Power to be better Fighters than the Fighter. Not to mention Polymorph and even martial stunts like spiked chain trippers!
Is it true, certainly, that other books could make the situation worse. Divine Metamagic could be horribly abused, and every time a new spell was added to the game, casters improved (especially ones who could cherry pick new spells without any real cost, like Clerics or Druids). Every time a new animal was added to the game, Druids got stronger (Fleshraker Dinosaurs, anyone?).
Attempts were made to power down some archetypes, and power up others, and a lot of largely useless dreck came with it- people remember the Incantatrixes and Planar Shepherds of 3.5, but you don't hear anyone going on about how amazing the Samurai or Green Star Adept were, lol.
And it wasn't just spellcasters- you got martial power creep as well, with uberchargers and wacky builds like Jack B Quick, the warrior who could attack you back twice every time you hit him (I can't remember the exact build, I think it used Karmic Strike and Robilar's Gambit and some other things).
Yes, sifting through all the dreck could allow one to unearth powerful building blocks, that, when combined, could create absurd characters, like Hulking Hurler/Warhulks strong enough to break planets in half, but all of this only existed if the DM was sleeping behind the wheel.
If a DM said "oh sure, all WotC books are fine" without looking at them, exercising veto power, and clearly outlining what the power level of their game should look like, yeah, you end up with some crazy results. But most groups didn't look like this. Many people who played 3.5 in the wild kept playing the game the way it had always been played. They marveled at how amazingly powerful the Monk and the Rogue were (I'm not being ironic here!) with "so many powers" and "look at all those d6's!". You had people proudly playing Barbarians and Fighters who thought Hexblades and Swashbucklers were weird and busted.
The Warlock class was seen as busted by a lot of DM's used to the traditional paradigm of losing power slowly over the course of an adventure because "OMG, they can Eldritch Blast and use their powers all day long!" without realizing that most of what they got, was really a pale imitation of what a traditional spellcaster could do.
I played with many DM's who felt that a first level Wizard being able to toss out a handful of d3 rays of frost was "WotC power creep", because they were basically a few free darts that ignored armor and creatures that had damage reduction!
It's not that 3.5 was any more or less busted than AD&D, especially by the tail end of Second Edition. It was just that the game was catering to a wide array of possible customers. You had traditional types who saw no problem with Wizard supremacy but were aghast at Sneak Attack being added to multiple attacks per turn (somehow ignoring how easy it was to deny Sneak Attack in the first place) and thought Fireball was the be all and end all of magic power.
You had people who noted the flaws with the PHB Fighter and were annoyed when it was eventually patched by a completely new class with the Warblade.
You had people who wanted to run epic battles of nigh-omnipotent characters who could challenge any monster in the Monster Manual by level 5, only playing with the sharpest, most expensive LEGO's in their builds.
And you had people who just wanted to play weird and different things, like psionic characters, Truenamers, and soulmelds.
And when all these people came into contact with one another, sparks flew, as it seemed like everyone was playing a very different game. Or worse, playing the game "wrong".
It fell to the DM, as it has always done, and will always do, to sort all of this out. But now the nerdrage was out in the open for all to see. You had people who were offended that, with a permissive DM and enough books, things that would never be allowed in their own games existed, and used that as a rallying cry as to why the game was busted and needed to be fixed.
And that's never really changed, has it? Look at 5e. I saw a lot of hate spilled on these forums over things like the Twilight Domain Cleric. It's too strong, it makes all other Clerics redundant, it makes it impossible to kill PC's (amusing, since I've heard that chestnut since 2014, so what's the difference?).
There are always going to be elements in the game that aren't going to fit with your vision, and your preferred style of play. Most DM's have at least six pages of house rules (and probably more) just to lock down what their vision and preferred style of play is as a result. Which typically involves nerfs and bans to "official" content.
And that's how it should be. Yet, somehow, the fact that a DM has to do this, has to exert veto power, is seen as some great burden. "Why can't TSR/WotC/whoever just make stuff for the game I want to play? Why should I have to fix their game for them?".
As if people who play the game in another way shouldn't exist.
That having been said, sure, not every DM has the time to vet every possible new idea. Some things really are just beyond the pale compared to other things. D&D has always had problems balancing it's various options*, because every person who has added to it has a different idea of what D&D is (and yes, mistakes can be made too, such as poor writing or editing). And you can risk having the game get away with you if you're blindsided by something you didn't expect.
Which can happen with things in the PHB, let alone splatbook #573. Now true, having that many splats out in the wild can certainly make things harder on a DM, and players can sometimes be put out when the DM says "no, you can't use this thing that's in a rulebook", but it's not a new problem. It's a very old one, and the answer isn't "make less books". It's about the DM and the players being able to communicate with one another and make compromises and admit mistakes, being able to move forward like rational beings.
*Without getting into what happens if the people who make the game actually try to balance things. Because each person has a different idea of what that looks like. Slow leveling Wizards with few spells at low levels, bad AC, d4 hit dice, and the ability to have a spell interrupted by a stiff breeze, forced to scrounge and scavenge for precious spell components to "earn" fantastic power might seem balanced to some. And might be seen as a horrible experience for others once you get said power, only to run into "save neg." on most of your spells, enemies with high magic resistance, immunities to certain spells and damage types, ever increasing saving throw values, antimagic zones, and the like. All while the Fighter is dual wielding +5 Intelligent weapons with an AC of -9, over 100 HP, 8 attacks per round while Hasted, and saves against everything on a 2 or better.
Just as examples.
