Agreed. The vast majority of the benefit is simply from learning to use composition over inheritance.

Most applications that aren't games don't need to support things like finding all active objects of a type or maintain many discrete actors executing their own run loops.

But Unity isn't dumping a lot of marketing into talking about the decorator pattern so everyone is jumping right to ECS now.

When performance matters I often find myself yak shaving existing code to basically turn it into structure-of-arrays format (like is required for ECS), if not converting to ECS entirely. The alternatives scale so poorly...

What were your problems with it? Was it using a particular library or engine, or you did it yourself?

I'm curious because I started using ECS-like techniques exactly because traditional OOP in games felt a lot like yak shaving.