With their ridiculous amounts of HP, it is always better to go in a party, and that’s good.At level 64, I found Bramble. Bramble has an AOE attack with an enormous (not even kidding here) range, and it’s very unlikely you’ll escape from it (so big you will most likely not outrun it unless you have some speed-boosting ability). I, as a level 57 wizard/wizard/linker, who for some reason is in level 60s zones, literally can get one-hitted if I’m not full HP, as out running it simply does not work for me. The Wizard’s Reflection shield also does not mitigate the AOE’s damage, and that’s just overkill as we can’t even outrun it. 
I dodged it once, but I think the hitboxes were just messy that time. He does like 1.4k~ damage, I have something around 1450 hp, so I was always left at 20 hp if I was at full HP.
Meanwhile my tank friend was going around taking the hits and losing only 1/5th of his HP.
The shock wave, I tried jumping above it, couldn’t avoid it, I tried going behind him and other blind spots, but it just couldn’t be avoided. It literally forces party play, unless I’m missing a way to avoid his AOE attack (which by the way has that red marker indicating that he’s going to do the attack, and basically covers the whole room).
I should also mention that his normal attacks had a huge range, a good range, the kind of range that makes you move smart and circle around the monster instead of just walking back.
That was a fun boss.
As for the others, I really do hope they make them harder in terms of speed and what not, just like you said!
Oh and I kind of wish the red markers that show up when they are going to attack disappeared on ALL of them, as some still have them.