The core of the STR hate is Nihilus. I am semi-engaged in the raid and try to avoid Nihilus phases. Why? Not because he is impossible, but because he is annoying. Annoying to the point of which I do not want to engage him. And the point of the raid is to be engaging.
The issue as I see it, is that there is too much defensive power concentrated into Nihilus. He has prot drain, he has prot regen, both on a very high, close to absurd scale. He also has buff stealing comboed with dispel. He also has a instakill that, while it can be countered, results in a kill all the same unless your hero has a heal or a healer goes right after for the save. There is also no way to topple him. Maybe putting the buff steal on Traya sabers, and one of the prot mechanics on Sion, would fix a big problem of this raid.
But one thing is certain. If Nihilus stays the way he is, people will keep being pushed away from this raid, and that is something that both sides want to avoid.