When I'm running as a damage role I always set tank as focus and attack their target unless marked otherwise. I don't understand why this is such a hard concept for many people; you don't have to view the main tank as the party leader, but they should be viewed as the battle leader (unless they are completely inept, in which case it's pretty much a free-for-all if they can't humble themselves to learn).

When it comes to tanking 4-man content, I can't be assed to mark since you can power through pretty much anything with i80+ geared and skilled players no mater what they focus or not. Tanking 8-mans is a bit different though; if the targets can be marked before battle I'll do it myself, but if they need to be marked as they spawn I'll ask for the most competent ranged player to do so to allow myself and/or the other tank to freely pick them up and snap hate w/o hesitation.