I didn't read that but the point is that you can't engage in an attack without creating forks, as monsterer said. The forks are visible. They would exceed those explainable by propagation delays, and would be selective against miners who include the banned transactions.

Collusion, in fact, doesn't even matter. It could be one large miner or a collusion. Either way it will be visible unless the collusion is total (maybe that is what your link states).

You would also, even in the case of total collusion, see transactions staying in the mempool forever despite having higher fees than transactions being mined. We don't see that either. There is no attack taking place. For the moment.