The next natural step will be - "Thanks for the comments, now the user needs to sort them by votes/date, ok?" and the URL starts looking like a query anyway, so you're on the way of re-implementing GraphQL. Then do you send avatars/timestamps/changeflags for all comments, or only on main body in this endpoint? Now you have the over/under-fetching problems.
The step after that will be "Oh there are 300 of them - I just want the top 3 comments first, and a pager for the rest ok?" and you simply can't do that with the structure REST mandates.
There is no structure that REST mandates, if there were it would be a specification and not an architectural style. There is nothing that says that you can't query for that:
GET /comments?sort=votes&limit=3
The exact string doesn't matter, what matters is the client can discover this. How HTML does this is by generating query parameters based on form inputs.
The next natural step will be - "Thanks for the comments, now the user needs to sort them by votes/date, ok?" and the URL starts looking like a query anyway, so you're on the way of re-implementing GraphQL. Then do you send avatars/timestamps/changeflags for all comments, or only on main body in this endpoint? Now you have the over/under-fetching problems.
The step after that will be "Oh there are 300 of them - I just want the top 3 comments first, and a pager for the rest ok?" and you simply can't do that with the structure REST mandates.