As warrior and paladin, I can say that it's not a huge issue. I've been relatively undergeared during story content on both jobs with parties brimming with max ilvl DPS. It all comes down to just pounding the AoE enmity generators a few more times and making sure you pick out the target the DPS has decided to focus on (not always the one you mark or start with). For paladin, riot blade keeps mana up for more flashing. For warrior, you can cross-class flash and mix it with overpower to lighten up the load on TP resource. I assume dark knight has it's own tricks to even it out.

The only tricky situation is when two high powered DPS decide to focus different targets. You either have to really lay on that AoE DPS or interleave your enmity combo (ie, alternate which targets get hit with #2 and #3). For single targets, tank's enmity multipliers are extremely generous. I don't think it would be possible for DPS to overtake you if you're using the enmity combo and your tank stance.

I do think it's kind of sad that older content is overly trivialized by high ilvl syncs. This seems to be an issue with lv 50 dungeons. Prior to that, I actually got to learn mechanics, but hitting the lv 50 stuff, every boss has become 'ignore almost all mechanics and burn'. I'm missing out on learning those mechanics. When I hit 60 content, I'm going to have some catching up to do. Nobody wants the pain of a minimum ilvl sync run. There should be a happy medium, like a min+20% ilvl synch for a double bonus or such.... of course, that would split the DF pool, so maybe ignoring mechanics on the lv 50 dungeons is acceptable, but sad.