In *theory* couldn't all their transactions be sybil attacks. All inputs except 1 for each mix come from them / known source. Every time the coodinator sees something coming in it has local wallets fill the rest of the space so to speak.
That would also be detectable, the minimum number of participants is 100 in a single round, and the timeout IIRC is 60 mins, unless the max figure is reached, I can't recall all the details but to make a long story short; the number of coinjoin rounds are guessable, a scenario like the one you described would make the number of successful rounds exponentially large.
Furthermore, you could use two identities at the same time and see if they end up in the same round or a different one, it would be pretty obvious for anyone observing wasabi to spot such an attack.
Besides, depending on your anonymity set target (they changed the name and the math behind the score but logic still applies) the coordinator would need to prepare all kinds of different input sizes to attack everyone, it is not feasible.
One way they might attack you is by signing the blinded outputs using a different private key, of which then they can brute force the number of unblinded outputs to figure out which input belongs to what output, I am not sure how Wasabi/GovSnacks Nacks prevents such attacks.