Of course mainstream ORMs leave a lot of perf on the table. For example, I once patched the ORM in a struggling php web app that i had to help. I started as a logger profiler thingy but then had the crazy idea of being a trace optimiser. By recognising the call sites from previous visits I could spot the 1+N and select * etc and actually transcode that into better sql in the next run etc. Shockingly it made a massive difference and I was surprised that normal ORMs aren’t doing that kind of thing.