Not reading seven page thread, or even the entire first wall-o'-text post, but here's my two cents:

If this were FFXI, aggro maintenance is a delicate balance that DPS and tanks (and healers, even!) need to be aware of.

But this is not FFXI. This is FFXIV, where SE has seen fit to give all tanks simply ridiculous hate tools. If a tank loses hate it's for one of only a very few reasons:

1. It's a low level dungeon, and the tank is missing most of their hate tools. In this case, it doesn't matter much. The enemies don't hit hard, and the healer should easily be able to keep themselves or others alive even if mobs stray.
2. The tank is hugely undergeared compared to the DPS. This is one of the rare cases where the DPS may be required to rein things in a bit.
3. The tank doesn't know what they are doing. There's not much excuse for this, if you're not new to the job.

Essentially, tanks are overpowered enough in the enmity department that in most cases, the DPS can do whatever the heck they want and the tank should still be able to hold hate. DPS all targeting different mobs? No problem: Flash, Overpower, Unleash, and cycle enmity combo. DPS blowing all their cooldowns at once and launching an overwhelming strike right off the bat? Standard tactics in high level fights, and the tanks deal with it just fine. Healers keeping Regen and Medica up during dungeon pulls? This is bad form, generally unnecessary, and the healers deserve a dirty look for it - but the tanks can still manage.

Things like DPS focusing on a single mob, marking kill order, or sleeping other mobs in the pack - these are crutches for early-game tanks. Once a tank gets some experience and more hate tools to use, they have no need of these things.