Just because there are some Muslims who have misapplied and abused takfir whether for political gain or otherwise doesn’t mean that takfir itself is illegitimate. Without takfir — i.e., delimiting exactly who is or is not Muslim according to formal theological principles and determinations as undertaken by qualified scholars — there would be no religion.
There are some that are trying to equate takfir with bigotry, racism, “othering,” etc. They employ liberal formulations in order to delegitimize Islamic categories and the Quran itself. Contrary to their (attempts at) distortion, there is a matter of fact about who is or is not Muslim, and our scholars have spent centuries elaborating on these distinctions. We’re not going to throw all that out just because modern people feel icky about religious authority, Divine mandate, and the imperatives that follow from submission to Allah most High.