I'm unsure wether or not the gems will remain the same, because as you've said as well, gems add way too much right now, a empty chestpiece with 3 sockets would be better than a chestpiece with epic stats. That's something I would definitely call a flaw and the fact that some item level 100 items have been scaled in favor of BiS item level 156 items, they can actually be better. I've noticed T4 has better stats than T6 for example.
Also the 2000 --> 1650 from the shield is simply the tooltip not being adjusted yet, as far as I know. I have the old Zul Aman trinket, the tooltip says 1635 or something and it does add 1635 directly, down from it giving 2500 armor on live. I currently don't like the shape it's in, because if I pop it I can burst someone down in a duel with one shield slam + revenge.
I've done Karazhan on 70 as prot warrior, could kill some mobs alone but required a healer for most, we did 2-man the boss (Huntsman) quite easilty, this was on beta. Also when I played on beta, it also said that the abilities of mobs haven't been scaled down yet, I'm not sure if this is also the case on PTR.