to pass as bicycles legally

Not even legally if you legally define ebikes as only being within the 3-class system. They only pass as ebikes at a glance if they're going slow enough at the time you look or can't measure their speed (granted, a decent cyclist can get those well past the 20mph cap were you get assistance even on flat paths and downhill gravity will do that with no assistance from the bike or rider, so it becomes harder to prove without just testing it out).