Some of the abyss levels are so hard they aren't even fun. Any advice welcome.

I'm having a hard time with boss levels in Abyss. There are so many enemies around them that it's hard to even hit them. I feel like all I'm doing a lot of surviving rather than playing (and that's if I can survive).

I've beaten around 10 tatos on D5 in the abyss, but some tatos don't seem strong enough, even with what I used to consider a great build.

Any advice?