Honestly our findings from working at scale (Facebook, Google, Twitter, Discord, Reddit, ...) were actually the opposite.
With hand written (not arbitrary) rules it's easier to understand the intent of the attacker and build a system that they can't work around because we're blocking them at their source of income. Sure they can figure out how to post messages but unless they can include their link/payload/etc it's not worth their time.
Machine learning defences are definitely a part of what we did, but they're slower to respond to attacks and generally easier to work around.
With hand written (not arbitrary) rules it's easier to understand the intent of the attacker and build a system that they can't work around because we're blocking them at their source of income. Sure they can figure out how to post messages but unless they can include their link/payload/etc it's not worth their time.
Machine learning defences are definitely a part of what we did, but they're slower to respond to attacks and generally easier to work around.