How is this making BA weaker when the blacklisting which you source from 3rd parties keeps the UTXO set constant through exclusion?
I don't know what you mean by "keeps the UTXO set constant through exclusion".
Wasabi specifically states that blacklisted UTXOs will it be allowed in the CoinJoin service.
A coinjoin makes blockchain analysis weaker because multiple users spend their funds in the same transaction, hiding which portion of the funds belong to each specific user.
This works as long as the users do not send those funds to questionable services where they can be traced again.
It's a cycle, not a decreasing line graph.