Only if your conception of better/worse is focussed on user count rather than user quality.
No, decidedly not. Unless out there there is an instance whose users are all all-around paste eaters, every instance has some users worth keeping in some conversation, furthermore political alignment says nothing about insight or competence in fields unrelated to politics.
A nazi is just as likely to know how to fix an obscure bug in some game or program than a tankie or a liberal, people are more complicated than their political allegiances and blanket removing an instance does us a disservice as much as it does them.
Refraining from defederation won’t change that.
Refraining from making the fediverse an archipelago where people refuse to talk to anyone who had the misfortune of picking the wrong instance is going to make that better, yes.
Not everyone who made an instance on lemmy.ml is a tankie. I almost did, and the only reason I didn’t is that they very gracefully and clearly state that Lemmy.ml is the flagship but not the largest instance.