In the spitballing suggestions…
What about a limit that they may not run for government on more than twice the HQ level.
If you’ve got HQ level of 10, you can run for office on 20 planets.
That limits the amount of nuisance one person can do. It’s still a nuisance, but it limits the amount of nuisance that someone can do. It also tends to not hinder established players too much (those who are most active in multi planet governance tend to not be getting that close to my suggested limit).
It’s not about political power as such… but rather a “do I have to worry that a person who is intending to disrupt play for people on a planet is running for office there?”