The parameters in prop=imageinfo themselves aren't very good. See T89971: ApiQueryImageInfo is crufty, needs rewrite. Ideally T66214: Define an official thumb API would be done, then the API could just point to that.
This is a pretty interesting problem to have come up with the new Core REST API in design process. Should we implement there, since we're doing new image info endpoints anyway? Does this make a good user story for Core REST API?
Whether this is implemented in the REST API or not, the feature request is still valid for MediaWiki-API.
Personally I wish someone would do T66214: Define an official thumb API. Then both APIs could just point to the image scaling endpoint for these use cases instead of having to define ways for clients to specify all the different thumbnail sizes they might want and then generate distinct URLs for all the different sizes.