Among his other winning attributes, Butker is in the "Jews Killed Jesus" camp.

One step above a municipal course.

Right, and it would require the complainant to identify the sincerely held religious beliefs they believe they are being discriminated against for holding. In this case, it would require Butker to acknowledge (or at least allege in a complaint) that the beliefs that triggered his dismissal were his beliefs regarding the role of women in society (etc). The NFL/KC would be able to pin him down and force him to either acknowledge that misyogny is his "sincerely held religious belief" or lose.

He, like everyone who wants to run to the rooftops to claim they are being cancelled, is holding up a shiny innocuous object and saying "look at how censorious and unreasonable everyone is being, silencing me for my beliefs" while refusing to acknowledge that the reason they are facing social consequences for expressing themselves is because the specific thing they expressed is worthy of social scorn.

Edit: Just to be clear, what my original point was is that it would be fun to watch Butker try to bring the discrimination claim because it would open him up to scrutiny that he does not want any more than the Chiefs want to answer the allegations. It would be amusing because he'd have to face, head on, the fact that the opinions that he is being criticized for are regressive, hateful, and not shared by the majority of society. He would fail in the effort that succeeds on twitter of conflating "I'm being canceled for being Catholic" with what he is actually being criticized for.