Have you tried Anubis or similar tools? I've had similar issues with bot scraping of a forum taking all server resources, and using PoW challenge solved the problem.

https://github.com/TecharoHQ/anubis

I did! It's very cool tech. However for our config it was easier to slap CF in front of it.

I will say one very appealing use of Anubis I'd love to try is using it as a Traefik middleware to protect services running in docker containers.