How often would a 12th level fighter be missing with a melee attack?
Use that as a better comparison, the fighter is probably still hitting more often (and doing more damage since he gets mutiple attacks per round).
Remember that a nat 20 always hits and a nat 1 always misses regardless of the actual number needed.
Also Dodge bonuses still apply and they always stack with other dodge bonuses.
Oh and don't forget the soft cover (+4 to AC) and firing into melee penalties (-4 to attack roll) when making ranged touch attacks - these "stack" by the way so shooting through a swuare that is occupied at a character who is in melee has an effective -8 on the attack roll. I was running a couple of warlocks and those get to be real pesky issues if you are not careful.
a level 12 fighter might not miss a lot, but against a dragon with an AC of 30+, he will still miss more often than the mage casting touch spells against the dragon's touch AC of 6 or 8.