Not done too bad, although I'll admit this is only off two leveling roulettes and like 3-4 duty supports.
The nervousness has shifted, somewhat - it's no longer general, now it's more specific. My only failure points in my runs have been purely not knowing boss mechanics. My large group pulls have been great.
So what it's coming down to is mechanics knowledge - both knowing my own toolkit well enough that suddenly jumping back 15 levels doesn't ruin me, and also knowing the bosses well enough to remember where I need to stand to not die.
Which... Kinda sucks, because that's going to be with me all the way to level cap, really. It's only a First-Tank-Job problem, I think, but it'll then be replaced by not knowing other Tank Jobs well enough, but that should also be easier to mitigate.
Either way, I'm enjoying Warrior! Can't wait to get some more abilities. Sub-50 is... Quite simple. GNB was fun when I tried the general lv60 kit, and I like what DRK is putting down as well.