So I agree with you, but the premises are quite restrictive.
What is a real concern, however, is the American government influencing world events in ways that materially harms people outside of America. That government retains its power through the ongoing global economic dominance of American companies. Ordinary people can't do much to directly affect global affairs, but they can at least choose where to spend their money, so why wouldn't they choose to spend their money with companies who aren't propping up foreign governments that harm them?
This point of view I could have understood 20 years ago, but Snowden revelations happened in 2013. Before that, US social media have always been censored according to US social norms.
Uncensored, un-backdoored services from a foreign country have never existed.
As for sovereignty, considering the current US admin as well as US tech barons have been pushing their horses in several EU elections, it's pretty obvious that services from a foreign country with such policies are an issue.
If, concrete example, e.g. Kagi doesn't censor or harvest data from or otherwise maltreat its users in any way, then what tangible benefit is it, to the European user, to avoid American-based Kagi, for so-called "sovereignty" reasons? What do they actually need, which is missing, that their democratic government can fix? For this question I'm not counting "other users are using it in a way I don't like"—I'm asking about the user themselves asking on their own behalf.