I actually DO think Mega Manectric could have been ordinary, because it's SOMETHING, while regular Manectric ISN'T something.
People say that Mega Manectric "ruins" regular Manectric, but if you ask me, it's an improvement. The main reason being that regular Manectric is just so...bland and boring. "Differently-colored canine with a weird head" is pretty much all Electrike and Manectric are. Mega Manectric feels like, you know, A THING (giant cartoon lightning bolt), whereas regular Manectric doesn't really have/feel like anything in particular.
It's funny, because I feel the exact same way with Persian and Alolan Persian, the only difference being that unlike Electrike, Meowth is distinct.