Of course, it's not a one-size fits all solution. I agree that ORMs are incredibly helpful and using them is almost always the right place to start for this sort of thing because they are very flexible and take away the cognitive load.
But we're talking about performance here... if/when you start to have issues, it is time to take a look and see where you can do better.
Rails' ActiveRecord gives you tools to help build queries whether or not you materialize them as full blown objects. If you need to do some specific data extraction but want to avoid a bunch of needless instantiation, you can still leverage the ORM to help build the queries (and avoid writing raw SQL as strings in your codebase) which is a very helpful halfway point.
But we're talking about performance here... if/when you start to have issues, it is time to take a look and see where you can do better.
Rails' ActiveRecord gives you tools to help build queries whether or not you materialize them as full blown objects. If you need to do some specific data extraction but want to avoid a bunch of needless instantiation, you can still leverage the ORM to help build the queries (and avoid writing raw SQL as strings in your codebase) which is a very helpful halfway point.