Earl of Cornbread
There's a significant problem with this analysis. The spells you're using in your examples existed back in 1e, doing much the same damage, when touch attacks were significantly different. Touch AC wasn't at all irrelevant back then because the full AC had to be hit. The simulationist aspects of a touch spell ignoring armor, natural armor, and shields made sense for the redesign in 3e as a concept - yet it made some touch spells like harm far more dangerous than they were in preceding editions (though in that case, the shift in hit point expectations didn't help matters). Dragons were suddenly vulnerable to a harm + magic missile combo like never before when not many clerics were confident enough to rush in with a touch attack and an only modest THAC0. I don't think relative damage from saving throw-based spells vs touch spells factored significantly into making touch ACs so low. I suspect they thought it made a good match for a wizard's low BAB and left it at that.Touch AC is nearly irrelevant, and intentionally so. 3e spells generally either required a touch attack or allowed a save, with the assumption being that the vast majority of touch attacks would hit but far fewer saves would be failed. That's why, for example, cause light wounds does 1d8 + level damage, while fireball does 1d6 per level.
Expending a True Strike spell to turn a single likely hit into a near-certain hit isn't an unreasonably trade-off.
Of course, they then promptly dropped in loads of ways for Wizards to boost those save DCs to unbeatable heights, or they didn't follow their own conventions about spell damage (leading to madness like shivering touch), but that's another rant.