Facebook is still a Delaware company, with lots of established case law for what Zuckerberg can and can not do, voting majority or not. SpaceX is now some Texas corporation with a state legislature ready to enable whatever Musk wants.
Though (at least to my knowledge) Zuckerberg doesn't have a history of abusing his authority to make deals that advantage other companies he owns at the expense of Facebook.
E.g. SpaceX buying up large numbers of Cybertrucks Tesla couldn't sell at MSRP, not even negotiating a good fleet sale deal.