on-chain tumbling can be effective at obfuscating the source of funds and making outputs fungible again.
There may come a time where mixed coins will be regarded with suspicion precisely because their fungibility has been restored.
the oldest mixing algorithms have long since been broken but blockchain analysis companies are always a step behind. effective tumbling means that observers can't tell with a great deal of certainty that outputs came from a mixer at all.
at the same time, exchanges have a strong interest in retaining fungibility, otherwise their liquidity is dead. the key is to avoid
obvious association with prohibited activities.
case in point. wasabi wallet's coinjoins are blatantly obvious, which is not as much of a problem for centralized mixers with superior liquidity:
one drawback of wasabi wallet is that it's blatantly obvious you are using a coinjoin because it enforces a 100-anonymity set. another is the ~0.1BTC minimum. it's definitely cheaper than swapping to monero though.