This is true, and I think even without payjoin or coinjoin this principle still holds up - over time, as coins circulate, and newly mined coins make up less and less of the supply, it will be virtually impossible for any coin to have not gone through something that analysis would mark as "shady" in the same way that most dollar bills have probably, at one time or another, most likely been used to buy drugs or pay hookers or whatever else.

I still prefer to avoid CEX's if possible, but it's a valid point that this method of analysis will inevitably become useless as coins circulate. The algorithms will have to be adjusted so they only flag coins that are directly correlated with blacklisted wallets or something.