occasionally when an instance is full of toxic trolls
Isn't that exactly what we're talking about? I get constant lemmy.ml lunatics jumping on threads, name calling, talking nonsense, posturing, telling me to "go away" (this is the Fediverse looney, you're only viewing my comment by your own consent), etc.
I've already user-blocked hexbear and lemmygrad, lemmy.ml is the next candidate for me.
Only if your conception of better/worse is focussed on user count rather than user quality.
Refraining from defederation won't change that.