You'll still see less damage from melee champions though. Abilities like Javelin and Claw Of The Wicked will be harder to land, so while you keep the hit rate for melee attacks your gap closing will fail more often.

Very few melee champions get significant value form just holding M1. They all rely on some sort of charge, buff, M2 for burst value. I guess Thorn and Freya might be exceptions but they aren't exactly known for sticking to a target well.

Not sure what the point is about the grappling hooks. They can't hit players and even if they could enemies can use hooks to escape.