Actix-web uses the single threaded Tokio runtime per physical core. This architecture is harder to design for than multi threaded async Tokio. Performance gains aren't worth the effort.
We use the same design for a product at $dayjob and have had no difficulty in designing for it. There is a lot of benefit from being able to use Rc and RefCell instead of having to go for Arc and Mutex. (Of course it's best if it can be written to not have any RefCell / Mutex at all.)
