In my experience, most tanks don't mark things in endgame. I do think after a while you sort of get a feel with what you should go after in what instances, and a lot of players that are level 50 now have been level 50 for a rather long time. If you'd prefer the tank to mark enemies, it never hurts to ask. On the rare occasions I play pally these days, I usually just forget about it but I don't mind if someone mentions it. If they won't or can't, then just go for whatever has the lowest HP in trash mobs. For bosses, just ask and if you attack the wrong thing and no one explains after asking, that's not really your fault.

Unfortunately, it sounds like you just got really unlucky and got an awful LotA party which...honestly, is the rule more than the exception these days. :/ Like others have said, most players would never bother with it if not for weekly caboncoat/carbontwine. That includes myself honestly, but I actually love LotA aesthetically (much more than ST or WoD) and think it's a fun raid at its core...but people do a lot to ruin it. Don't let it get you down. Try going in with a full or mostly FC party. That's an easy way to get more out of it.