I'm sure it depends on the complexity of the app you're building. For simple crud-ish apps (ecommerce, online auctions, etc) I've found that I don't need to write even a single line of custom SQL, and performance is generally good (lots of N+1s, but these are easy to avoid with things like bullet). I also love being able to let Rails render most HTML, and the few things that need to be very dynamic you can just throw a single react component in without worrying about the usual SPA problems.
If you're just prototyping stuff, I don't think you can beat Rails for productivity. But if you're targeting something more enterprise or large scale, I don't think it's a good choice. Go/Rust are so much faster (not that that matters a lot), and even things like C#/Java pretty nice to use nowadays.
It is a gem that tells you when you are accidentally making a N+1 query and suggests the best way to fix it in AR (it also tells you when you have over used includes that are not needed and other such tweaks to make to your queries).
If you're just prototyping stuff, I don't think you can beat Rails for productivity. But if you're targeting something more enterprise or large scale, I don't think it's a good choice. Go/Rust are so much faster (not that that matters a lot), and even things like C#/Java pretty nice to use nowadays.