I agree with that much, but using GTK+ in the normal way for your language has a much lower cognitive load than any proposed alternative.
> BTW I work on a project that made this same argument years ago, writ large, for the CI system they built. "Size doesn't matter; just throw more money at instances; its cheaper than spending dev resources to make it efficient." So, now we have a development pipeline that uses more EC2 instances than production, by a factor of about 100. The build no longer runs well on (very fast) dev machines, and takes 30 minutes even on xlarge instances. The build is enormous, complex, and slow, and it was allowed to get that way because someone made the same argument you are making against a strawman.
That's a textbook slippery slope fallacy. If and when resource consumption becomes a significant issue for your use case, take measures to address that. Size absolutely can matter. But 120mb does not matter.