I've seen this comparison made before as well, and it's still not a great representation of the situation.
All that really differentiates the ARMS cast from each other (in gameplay) is a difference in their stats, size, and gimmick. Spring Man, for example, punches in the exact same manner as Ribbon Girl, who punches in the exact manner as Min Min, who punches in the exact same manner as Master Mummy, who punches in the exact same manner as Dr. Coyle. 90% of the moves an ARMS character can perform are shared with the rest of the roster.
Compare with the shotos, who share comparatively little of their kits amongst each other. Ryu punches and kicks in a way different from Akuma, who punches and kicks different from Sakura, who punches and kicks differently from Dan. Even then, the abilities that these characters do share are completely different in appearance and function between the shotos. Even though Ryu and Dan both hadokens, how they do so and the effect those hakodens have are night and day. If the shotos were like the ARMS cast, they'd all perfectly share Ryu's punches, kicks, and specials while having different stats and one unique special each.