Is “diversity hire” a slur? If not, then why don’t we question the competence or qualifications of non-POC hires? Like why are non-POC hires not “cronyism hire” or “familiarity hire”?

In a vacuum, I wouldn't consider "diversity hire" to be a slur. However, in colloquial use by racists and bigots, it is definitely used as such much in the same way they have appropriated "DEI" as a slur.

To clarify, I mean the terms themselves used in the proper context. Calling someone a diversity hire, DEI hire, affirmative action hire, etc is 100% appropriating those terms as slurs because it calls into question the target's qualifications by insinuating they were only hired to tick a box.

why don’t we question the competence or qualifications of non-POC hires? Like why are non-POC hires not “cronyism hire” or “familiarity hire”?

We totally do:

• Familiarity hire: We call those 'nepo babies' or something related to nepotism.
• Cronyism Hire: Not sure there's a single term for it, but I (and probably others I'd imagine) just literally call them "cronies".

They are, it's called "Nepotism".

"We are all family in this company" -> We don't have non-white relatives.

I am kinda sick of seeing people get unfairly criticized or sidelined

Just curious what you're going to do about it, if anything?

If you know and understand all these abbreviations and special terms, then you are deep in the mud already. To know if this or that may be a slur cannot rescue you anymore.

I suggest to look for a whole new circle of friends.