I am very average when it comes to PvP and I have close to a thousand kills with Hand Cannons with most of them coming by way of Vanguard purchased version of The Devil You Know. It is a perfectly fine PvP weapon.
I only gave it up when I got The Last Word and decided that my alternate PW should probably be an Auto-Rifle since my new IB boots provide more ammo for that weapon type.
The OP is saying that there was no reason to remove something from the game that wasn't broken to begin with and only became "broken" when this new feature was added since there was the potential for PvE players to convert Vanguard Marks into Crucible Rank
He has a very valid argument. PvE players didn't break this system. Quick fixers that don't venture further than the Divide for Spinmetal did.
I don't agree with most of his arguments because I think that strict PvE players are only enjoying half of the game, but that does not invalidate his opinion.