Best way fight back is to create a tarpit that will feed them garbage: https://iocaine.madhouse-project.org/
Ten minutes later, the ball is back in your court.
That doesn't match my (albeit limited) experience with these things. They are pretty good at other things, but generally squarely in the real of "already done" things.
Claude is happy and able to provide a laundry list of ways to mitigate the impact of tarpits on your crawler, and politeness / respecting robots.txt is only one of them.