Edited OP to remove last point. But I'll support it here:

XMR has adaptive block size. If massively adopted, the chain will bloat to ridiculous levels and it will become more difficult to run a full node. This hurts decentralization of the project. Currently, chain size is way smaller than BTC but that's because it's barely used. Thus the anonymity set is currently small.

Another critique: mining with general purpose hardware is a decentralization gain at the expense of a security weakness.

CPU/GPU mining is good for decentralization because more people have access to the hardware.

However, ASICs are good for security because almost every ASIC in existence is currently utilized to defend the network. There isn't a lot of "spare hashpower" to devote towards a coordinated attack.

Whereas, every CPU in the planet not currently mining XMR (probably +98% of all CPU cycles) could be persuaded to attack. I've heard XMR shills say that it's a good thing because in the event of an attack, people will magically decide to defend XMR and start hashing cooperatively. But it could go either way.