This is pretty fun game analysis. I hadn't considered slow validation from the perspective of a miner carrying out the attack. I also didn't expect the attack to be profitable but it succeeds at being profitable if bitcoin is succeeding (miners are capturing a lot of fees). This is the scariest kind of attack because it's sustainable.

> Thus, if such an attack were to occur, the attacking miner would not suddenly become the dominant miner for all blocks, but they likely WOULD become the only miner including transactions in blocks. As such, we'd expect the on chain transaction throughput to plummet, causing the supply of block space to plummet, and thus if demand remained the same then the going rate for block space and thus transaction fees would spike rather high.
>
> As such, the expected profitability from such an attack would be excess transaction fees achieved by essentially cornering the market for block space. This could potentially be a fairly profitable attack if it is conducted during a time in which demand for block space is already high.