So I've been playing Zombies since the good old days of WaW and I've always loved Double Tap, both the original and 2.0, and obviously I agree that 2.0 is superior in every facet but I don't think the Original was a bad perk either.
Everyone always complains that OG DT made you waste ammo, my response to that has always been "Skill Issue" because yes it increases Fire Rate 30% but that doesn't mean that it innately makes you waste ammo, if you actually land your shots then it increases overall DPS making it a God send for slower Firing weapons like the B.A.R. and the Browning M1919 in WaW and the HK21 in BO1, more over it's amazing for Semi Automatic weapons as it allows you to shoot faster and raises the shot lock cap and it cycles the Bolt on rifles and Pumps shotguns faster as well.
Overall like my title says I definitely think Double Tap was over hated, would I take it over DT2.0? Obviously not, but your damn sure I'm going to take it before something like Mulekick which until recent games would end up being a huge Point sink when you inevitably go down and lose your 3rd (probably PaPed) weapon.