Exactly. The extra small round sizes in Whirlpool makes it far easier to attack than coinjoins that include hundreds of coins into one round.
But, far more difficult and expensive the more the victim remixes.
Wouldn't it be concerning if it was only one premixer? One remixer isn't going to harm.
- If the other four premixed inputs belong to an attacker, then they know the respective remixed UTXO, which isn't crucial in and of itself; it'd be if they could work out the remixed input's past.
- If less than four premixed inputs belong to an attacker, then they know even less than that.
This fee does nothing when the attacker is also the coordinator.
I was talking about Samourai's coordinator.