I don’t think that there’s a single correct answer for that. Each case is a case; you need to balance how important are your political views vs. centralisation for you, and decide your course of action.
A few highlights:
The difference between a bag of spilling versus putting your eggs in different baskets is just point of view. More comms about the same topic = if one of them goes down, the others still survive.
Users can subscribe to multiple comms with the same topic. That’s what I do with cooking comms, for example - !cooking, !cooking, !food, I’m in all of them, and I (as a user) see no problem with this.
Somewhere down the road I predict that the devs will going to allow users (or perhaps the mods) to “group” comms across instances, to visualise their content together. So the bag of spilling will get better over time.
Remember that comms don’t just abide to the instance rules, they also set up their own rules. If your issue with the instance is that it lacks a specific rule that you feel to be important, you might want to talk with its mods to actively set that rule up.
Based on that I think that the problem is smaller than it looks like. If you don’t like the comm about that topic, for whatever reason (including the instance that it’s hosted on), by all means, create another elsewhere.