Scale can come in any size you desire it's just that the large ones seem to fly better but it depends on the design. WWII fighters should be larger to apply all the details which add weight.
WWI aircraft as well as Golden Age aircraft have designs that work as well as trainers. Example the Curtiss Robin has dimensions and design that would flatter a 20th/21st century RC trainer. A bit of dihedral 1 or 2 degrees, not really enough to notice, would probably make Lindbergh's Spirit of St. Louis flyable. Either that or aileron differential. The scale Piper PA18A is a duster that has a lot of scale add ons such as dust spreader, spray booms and wind driven pump. It too should have 1 or 2 degrees of dihedral but not enough to notice.