It depends. Rails is great for rapid application development. You probably don't want to decouple at that early stage. But when your app struggles with slow responses and job management becomes increasingly difficult, you begin to see the flip side of the trade-off between ease of development and performance. This recently featured project, https://github.com/9001/copyparty, is extremely performant but foregoes many of the niceties of Rails. It uses the filesystem instead of a database and has no build step for assets. I'm not sure the solution is to push all queries into repositories, but it's quite easy to abuse the convenience of ActiveRecord by intertwining all the business logic and database access.