> I work on a large product with two decades of accumulated legacy, maybe that's the problem.

I'm in a similar situation, and for the first time ever I'm actually considering if a rewrite to microservices would make sense, with a microservice being something small enough an AI could actually deal with - and maybe even build largely on its own.

If you're creating microservices that are small enough for a current-gen LLM to deal with well, that means you're creating way too many microservices. You'll be reminiscing your two decades of accumulated legacy monolith with fondness.