Semantics are 90% of programming though. Learning syntax is simple, learning semantics is hard. Semantics structure how you think about problems and express solutions.
The question is about a performance benchmark. From a performance standpoint, rpc and rest are the same (http requests that execute code on the server).
The "semantics" you assign to one or the other don't change the technical details about implementation and performance.
It's the same payloads with a slightly different command format if you structure your program in exactly the same way. The point is that you don't structure your program in exactly the same way in each case.
There is no difference: neither of those are REST.
Calling an URL with an action in the path name (rather than a resource name) is technically not done in REST -- the action is expressed through your HTTP verb.
Using GET/POST/DELETE directly does not mean you're doing REST - there's a whole set of rules and assumptions that come with it.