Seeing as how I still haven't figured out how "aggro" works in GW2 I'd also lean towards "chaotic". I've mentioned this before, but there have been times I've hit a champion once and it stayed on me no matter what until I was downed. I quit attacking when it appears I have "aggro" out of habit so even not doing anything past the initial hit this would happen. Plus, many, many times I'm doing an event and I know for a fact there's no way in Hell I'm anywhere near top DPS because I have gimp gear/build, I still get things on me that are near impossible to shake.
There just doesn't seem to be any rhyme or reason to mobs attacking you so, yeah, I consider that "chaotic". I've also had encounters where resing people is enough to get "aggro" for the rest of the fight, so while I would normally assume that's some kind of "healer aggro" I have no idea in this game.
Somewhat related, I do think the healing in GW2 is too weak in many cases. Using the examples above of simply being unable to shake "aggro" there just isn't enough healing or endurance to get you out of it. You can only dodge so many times, it's not like it's an unlimited resource. Very few classes have "aggro dumps" either, so basically you can try all you might but inevitably the only way you're ultimately going to get something to leave you alone is to get downed and even that's not enough sometimes. I still see people "tanking" while in downed status.
Having said that, I'm not a fan of the trinity either. I'd really like to know what non-MMO RPGs that one guy plays where he still sets up his characters in a trinity because I never do that. I almost always set up my parties as groups of hybrids. Likewise, in WoW I almost exclusively played hybrids. I like being self-sufficient and not being SOL when one of your dedicated/role-specific people hits the dust because they're so fine-tuned into one area that they can't handle anything else.