I gave Mastodon a small chance a couple weeks ago and just hopped on Lemmy today and I can already tell (at least as of right now) I prefer Lemmy as a platform. I’ll definitely give Mastodon another chance but I just couldn’t really get into it. I think I agree with you on the fact that the content seems to federate better on Lemmy.
You can still access and interact with communities in other instances even if you signed up with the Lemmy.world instance. Not sure if that’s why you wanted to create an account on another instance or not. But as the other user mentioned, there should be a way within settings.