we have an actual leftist party that has legitimate chances
We do not. The NDP may have actual leftists among its membership, but it hasn't been a leftist party in 2 decades now. It's a neo-liberal party focused on courting an urban professional class and denying any and all claims that they are "socialist".
Federation isn't a mess, it's just... messier. And too many federated services do their damnedest to hide that they function differently, meaning people treat them like they're perfect drop-in replacements.
It results in a lot of questions about "Why can't I ____?" and answers of the "Because this doesn't work that way" variety.
Like, look at Mastodon. It bends over backwards to hide the fact that it's 10,000 different websites. The result is that people could not understand what the big deal was, nor why it wasn't as easy to see everything from some other website as easily as they could from a single website that everyone was using.
This further led to centralization of the Mastodon ecosystem, which... I mean, at that point, you're just abandoning the central concept.