No one really considers crypto held in exchanges as decentralized, I guess some might but it's pretty standard knowledge.

Where coins are held is completely irrelevant. There are cryptocurrencies on real blockchains, and while the technology is dumb and mostly useless, nobody denies that PoW and properly implemented PoS are decentralized.

And then there are centrally issued and controlled coins on private, permissioned ledgers a.k.a. databases. But most cryptobros never cared about the technology nor the political goal, so anything can be called a cryptocurrency as long as it's a medium for gambling and speculation outside the regulated financial framework.