XI tanking had everything to do with tempo. You had to manage your casts inbetween enemy hits, whereas here you will mindlessly spam certain skills, depending on single/multi-target etc.
Even more so, no utsusemi, no cures, no nothing. Use your skills, manage your defensive CDs and that's about it. It's as easy as it can get if you were used to the tanking of XI endgame back in the old days.
Marking is more or less useless, only good if you're undergeared for the content. Otherwise, build multi-target threat (through Flash, Circle of Scorn, Overpower, whatever's your job) and have your DPS go happy casting.
In FFXI you had to sleep mobs and so on, here it rarely is an issue.
You will find situations where it is useful / necessary to mark mobs though, so make sure you have a hotbar ready for it, just in case. But I personally don't bother with it 95% of the time.
