About removing restrictions from casters; the reason this occurred wasn't just to make casters more powerful, it was because the game didn't work as advertised. From the very beginnings, Wizards were critical party members that needed to be protected because their power came at a cost. In your classic dungeon experience, warriors and clerics were up in front, and wizards stayed in the back, using spells oil or thrown darts/daggers; the idea was that they wouldn't be at risk very often.
And if they were, there was a plethora of powerful defensive spells they could access.
The 3e design team noted, however, that the rules of D&D didn't actually support this paradigm; casters were very vulnerable. Adventures now took place outside of narrow corridors, a wall of meat standing in the way wasn't always viable, and a thrown rock that does 1 point of damage could prevent wizards from doing anything at all, meaning people would play them less and less. And the game is meant to have a balanced party of warrior/rogue/priest/wizard.
So concentration checks were invented to give the wizard a chance to actually use their spells when bereft of a useful meat shield, since the reality was, there was no mechanic that let a warrior actually prevent the wizard from being targeted. And, in fact, most attempts to give warriors these mechanics have been rejected by a vocal part of the community (see any discussion about marking or taunting effects being "mind control" for details).
Thus we have "tanks" who can't actually tank very well outside of very specific and easily exploitable builds. As a result, casters were made more durable so that less effort needs to be devoted to protecting them so that they can actually contribute to combat.
Rogues benefit from this as well; we went from the Thief being barely more survivable than a Wizard to justify their utility to being able to drop a handful of d6's on enemies in combat.
TLDR; these changes weren't made on a whim with an idea of making casters gods, it's an ongoing evolution of trying to keep classes viable in the face of the actual play pattern not being supported by the rules, and objection to certain attempts to remedy the situation.