Right. If you write SQL directly, you can also use commands such as EXPLAIN to see what the lookup strategy will be. If there's a full table scan of a large table involved, maybe you need a different query or a new index. If the SQL generation is hidden by some library, you can't do that.

Wikipedia runs on MySQL. They have replicated read-only copies of the database and ngnix caches which handle most read-type operations. Is your site busier than Wikipedia?