Hi OP, and welcome to the forums! These are some really frustrating scenarios you're putting forth, but hopefully we can help you figure out how to cope with them like we have.
This bothers me, too. So often, enmity and hate feel like an arms race, and when DPS get a head start, it can be especially difficult to pull off of them. If it's obvious it was a mistake, or if it only happens once, I'll usually forgive it, but more than that, I start to get into the mentality of "if you wanted to pull, you should have queued as a tank." I usually ask nicely if someone keeps doing it to please let me pull, and that works ~80% of the time. If they get mouthy, though, or just ignore me, I start letting them tank whatever I can't get off of them.
This one is less annoying, but does still cause problems. If a healer throws Regen on me right after the pull starts, there's a good chance the first tick is going to rip hate off of me. It's one thing if they stand still, because then I can run to them, cover them, and flash until my enemy list is lit up red, but if they start running around, it can make things horrible. And what's worse is that sometimes, right clicking on the buff doesn't take it off.
AoE is less of a problem, though, because usually the potency is low enough to where regaining the hate isn't too difficult. I usually just position myself just outside, and try to time Flash such that it will hit the mobs as they run past, and it usually works.
Unless it's at the beginning of a fight, you're not very likely at all to lose hate during the time you're dodging telegraphs and AoEs. Most of the time you'll have a comfortable lead, and unless they save their offensive cooldowns specifically for that point, they're not going to be able to take the lead. It might be annoying that they get to do stuff while you need to dodge, but it shouldn't really impact your gameplay too much.
Also worth noting: once the AoE market disappears, it usually means you're safe to resume your position. The animation might look like it's hitting you, but whether or not you're hit is calculated when the castbar/marker disappear. This gives you a few more moments during enemies' animation locks to keep things in place.
Usually if I'm struggling (which happens increasingly less frequently), I'll throw the DPS in question a compliment, and ask if they can help me out. Something like, "Daaaaaaaamn, Daniel! Back at it again with the leet deeps! Making me work for my hate! Mind helping me out a little?" Sometimes they do, sometimes they don't. But in all situations, I take responsibility for enmity. Even if they should be paying attention and being prepared to own up for their massive numbers, most DPS will think it's not their problem, because "enmity is the tanks' job." Which is a stupid attitude, but I digress.
This is an unfortunate side-effect of open-world content vs. group content. When a DPS or healing job gets hate in the wild, they survive by kiting. The game trains them to run away when they're being attacked, despite it being opposite of what they're supposed to do in a dungeon setting.
If you marked, they have no excuse; if you didn't mark, you have no right to complain.
Even when marking, though, I am astonished by how many DPS jobs completely forget how to count. Sometimes it isn't a problem, though, and if that's the case and I can hold hate without their cooperation, I'll leave them alone. If it IS a problem, I'll usually start asking in general if people can follow the markers. If it persists, I'll call out the offenders by name. If it still persists, I start the vote-kick.
And you've arrived at the main reason why people don't want to tank. It isn't true that tanks are solely responsible for the smoothness of a run, or that tanks should be blamed whenever something goes awry. A good tank can sometimes prevent things from going poorly, and can clean up others' messes, but group success relies on everyone in the group. A great tank can sometimes save a run, but so can a great player in any other role.
Wrong, wrong, wrong, and wrong.
Tank gameplay deals primarily with enmity. When we go through an encounter, it is what we focus on. However, it is something DPS jobs and healers need to be conscious of, as well, because if you aren't a tank and you get and hold hate, there is a very good chance you will die, which places a 100% damage debuff on you until you come back to life. Tanks focus on it primarily, but this absolutely does not mean DPS and healers get to ignore it. That's why they have enmity-dumping tools.
Tanks are good at generating enmity, but they are not gods.