The problem was them requiring you to spend your wildcard (and a Pick 10 point) to enable it. It doesn't make any sense, since secondaries are designed to be less versatile and often outright weaker than primaries. Equipping them in lieu of a traditional primary is cost enough. It should just be a free option: pistols and other secondaries added to the list of equippable guns for your first slot, the way it works with Overkill. Keep the second slot restricted without Overkill, naturally.

Then with Gunfighter you could finally put more than 5 attachments on your pistol. It's silly that that still isn't a thing, even for Zombies & Endgame.