Yes, I've done Dynamis - Buburimu. I've beat it. That NM is weakened by defeating NM's that lock his abilities. Dynamis - Valkurm work the very same way. However, those NM's are up from the start, and are in the same zone. they are not pop NM's, like in sea. On the other hand, these NM's drop weapons 100% of the time. I doubt its a coincidence.
Either way, you can't compare AV to him and come to the conclusion that AV is broken because killing the other NM's doesn't lock his abilities, like it do in a completely other zone and expansion pack. Comparing AV to AB is like comparing apples to bananas and say that bananas have to be broken, because they don't have the same shape and taste.
For all we know he were broken before, causing his abilities to get randomly locked by NOT doing what you're intended to do. Just because people haven't figured out what to do yet doesn't mean its broken.
You can compare it to Parade Gorget. People assumed it were broken, unreleased, or not ment to be obtained yet, just because no one had figured out what to do. Eventually SE told us what to do, and then suddenly everyone have it. People assumed that the Strange Aparatus were of no use and inactive, untill someone figured out the secret password. Do remember that no one had figured it out for a long time. Roughly 2-3 years if I remember right.
Just because no one have figured out how to beat him, does not mean he's broken. You can't come with the assumption that he's broken just because they fixed the only known way to kill him. People relied on a glitch and bug to kill him, it was obviously not the way he were ment to be killed. I repeat, Just because people haven't figured out the true way to beat him, does not mean he's broken, nor unbeatable. That's that.