The good reason was that queries were not optimal and when we came up with optimal ones which were not following the access pattern or syntax that activerecord introduces, then the excuse was “…but activerecord…”.

If i was a dev i would appreciate some data guy’s opinion in queries, indices, etc while my db crashes every now and then, but it’s either a power play/politics thing to ignore the new guy or the ‘i know activerecord/hibernate/kafka/whatever’ thing and i won’t bother sith anything else that will solve the problem.

It's a tradeoff. Everything is a tradeoff...I think ORMs like ActiveRecord do make the code easier to reason about in most cases and are worth the performance hit. All abstractions cost us performance..we could be all writing on bare metal C/C++ but not many web shops want to do that.

There isn’t really a good reason to avoid ORMs in the general case. You can log the actual queries just fine.

In my opinion bad performance comes from inadequate knowledge of a sharp edged tool