Well, one thing is that characters that lag behind in AC should -probably- get the magic armor first. Given that +2 equipment's been available in parcels since level 2, there's no reason he should have only a +1.
It's not much of a difference, but that, plus leather armor proficiency makes a huge difference for sorcerers.
For a 5 PC group, the DM only hands out 4 magic item parcels per level. There's only 10 6th level or higher parcels total before acquiring level 6.
With the standard 5 +2 weapons/implements, 5 +2 armor, and 5 +2 neck items for the entire party, you are assuming that this PC should rate +2 magic armor before he rates +2 magic weapon/implement or +2 neck item or before the other PCs rate them. I just find the concept of the DM handing out magic items first based on who has the lowest AC or defense or to hit a bit metagamey.
This also does not allow for any magic items of level 6 or higher that are not the big 3, nor does it allow for many levels of playing with a cool +1 item before it is swapped out with a +2 item. For example, it will take 4 levels just to hand out the first 10 +1 items. If the DM hands out +1 armor to the Sorcerer at level one or two to handle the AC discrepency at lower levels, the Sorcerer won't be keeping the +1 amor long if he acquires +2 armor at level three, four or five.
As for Leather Armor proficiency, I absolutely dispise that feat tax. Although the game is playable without it, it's a pain in the butt. I play a Sorcerer over on LEB who did not take Leather Armor and she gets hit nearly every time a foe attacks her. Not that Leather would help too much with that, but it's still a design weakness.
I just don't think there should be any "must have" defensive feats in the game system.