Being a much smaller man works out if you're performing martial arts, but wrestling is highly dependable on brute force and being able to mobilize your opponent. The only way I'd buy someone like Adam Cole manhandling a guy like Lashley is if Cole was Spiderman.
Like others have said, he should only be selling for the absolute top little guys, guys in the main event. Him selling for guys like Finn Balor, Samy Zayn and Humberto Carillo is ridiculous. He should be squashing those guys.