billd91
Not your screen monkey (he/him)
There are tons of problems with tier 1 caster (many of them outlined here). However, one of the main problems with tier 1 casters versus martial melee characters is the Action Economy framework of the 3.x/PF system. The action economy of casting a spell is bound up in standard actions. Spellcasters' payload scales along the paradigm of the standard action as they level up. However, this is not the way for martial melee (ranged manyshot excluded) characters. Their payload is bound up in the full attack action and therefore scales with usage of that action economy framework. As such, forgoing a full attack in order to leverage a move action and a standard action becomes more and more punitive as the game progresses; punitive to the point that anything other than standing in front of an enemy and rock-em sock-em full attack routine is costing you and your group in the action economy game versus your enemies. In a game as swingy as mid to high level D&D, that is a very, very bad idea. Further, the same goes for monsters with multi-attack routines that rely on full attack actions; the main reason why high level enemies have to be casters because kiting/shutting down melee enemies is a joke...and the reason why dragons go from being dragons to...well sorcerers.
Why they went this route, I don't know. Standardizing the action economy in 3.x/PF would address a few (not remotely all) of the problems between casters and melee characters (however, it would also help casters in the summon game and when they want to turn into fighters themselves...). Further, it would create more dynamically mobile combat, more room for tactical depth, and less action economy relevant trap feats like spring attack. At the end of our 3.x days, I had brutally house-ruled the system (including removing full attack actions and standardizing the action economy) such that it actually looked like...well, 4e.
I don't think it's particularly mysterious why they went this route. It's historical. In 1e and 2e, PCs who weren't in melee contact with their opponents had to close first, and if they had to do so, they were allowed a melee attack. In 1e, within melee contact is within 1" of scale (10' indoors, 30' outdoors). In 2e, the rule for movement and melee says characters can move half their full round movement rate and get a melee attack. In neither case does it state that the PCs can get their full melee attack rate or melee attack routine. It's just a melee attack. 2e's rule translates quite well into the move action/standard action formulation for 3e.
The big question is why did spellcasters, who used to be unable to move or gain their Dex bonus in a round when they are casting, suddenly get to take a move action along with most of their spells? That's the real change. My guess is it was the unfun complaint. So they removed those two drawbacks. Then they included a Concentration check when hit so the spell loss isn't automatic. And then magic item creation. And then most differing spell casting times and their effect on initiative. And so on. Very few of those changes, taken in isolation, would undermine game balance (with the possible exception of magic item creation and some really cocked up prices). Taken all together, you've got a different animal for any player willing to exploit it.
For what it's worth, standardizing the action economy is a frequent remedy - but most often directed toward dropping the spellcaster back into a slower and more vulnerable mode. And I think from a simulative perspective, that works pretty well.