Something missing from pip is the ability to do upgrade --all like conda can do update --all in an environment.
Wrappers around pip that do this are oftentimes slow because python. Given that you already have some resolution strategies available, it would be really nice to see something like that. And it's also gonna be very fast in your case I believe.
The exact resolution strategy for something like that is up for discussion but I think resolution strategies like the one conda uses have been liked by the community.

Maintainer edit: See #1419 (comment) for a current overview of problems and solutions