Oh come on, the term itself is political. It has always been political everywhere: same in Russia and Ukraine.

You can't "politically charge" a term that has always been political. The concept of "native language" is 100% political, always.

As for "mother tongue", it has the same problems and more. "Mother tongue" brings in an implicit idea of 'less prestigious ethnic language', "mother tongue" as opposed to "father tongue" (even in ex-USSR: e.g. you would say that Belarusian is "матчына мова", but you'd never say that Russian is someone's "матчына мова" even when speaking about ethnic Russians — because Russian carries higher prestige, so can't be "mother's" language)

We should not try to replace "native language" with a different term, we should avoid it in serious discussions. Instead, we can speak of proficiency, parents passing language to children, the role of education, the ethnic language, the national language, etc.

And if we do so, we see that there's nothing wrong or unusual about Ukrainian.

If anything, it's huge languages like Russian or English that are unusual. They're different from 99% languages of the world. After all, bilinguals are more common than monolinguals. It's Russian that is a weird outlier, not Ukrainian.