I dunno, I help a lot of people kill T1s because I see one or two or three i117 people having trouble, unless they're on the right jobs and the best-geared within that that they can be. And the worse part is, the jobs change from NM to NM, unless you have such overpowered help that they can make up for improper jobs. ("such overpowered" is relatively easy to achieve, many many players are geared to this point)
Before someone trolls me about saying this stuff is hard, I don't find this stuff as hard at all, but I can see returning players stuck with nothing but returning players having a lot lot lot of problems.
The Rawhide NMs
Tengata Manu - Heavy wind damage, want an Aegis or a RUN, as well as a good whm with capped enhancing (not that capping enhancing is hard). I'm pretty sure she constantly dispels buffs, as mobs of that family often do
Vidala - Want a NIN tank (less tp feed) but Gessho will work. His stonegas don't hurt at all but you need nukers to delevel him when he levels up. PLD or RUN would probably work alright, but it's going to be harder than NIN or say dnc/nin. Trust nukers don't work because wind magic isn't 100% guaranteed to delevel him with each cast, and trusts cast pretty much whatever they want.
Gestalt - Want a PLD or RUN and attentive melee, dread spikes can kill a DD pretty fast if unlucky with TA.
Angrboda - PLD or RUN. AOEs can probably one shot melee DD in i117 gear without dt sets.
Cunnast - Lol, this guy. Back when my breath kit was around 35%, I was sometimes getting oneshot by him and so was Amchuchu.
I wasn't playing when Zitah came out, but I'm sure many groups did this in a mix of 119/115 gear (Delve/WKR/Skirmish/JSE) and did great but there's a wide wide difference between the quality of that gear and freebie Eminent stuff. I do know firsthand that returning tanks can't fall back on their 99 -dt gear because the lack of defensive stats gained from ilvl (eva/def, m.eva/m.def, bonuses to base stats, hp) really really hurts. I was, for about a week, stuck in this awkward place where my once-prized gear sucked, but eminent sucked too.
There is also, as we all know, a tremendous advantage having humans over trusts, most of the time, except when Apururu is in the mood to -na you as the debuff is landing or stunbot-capable Zeid and Ullegore.