They could of made them all do the same damage and solve that issue and make it about the utility they bring.
The issue they had was, venom amo had to do something special (they had it be a stacking dot like old deadly poison for rogues was), arcane amo did somethign special (extra focus generation), and frost amo was a pvp tallent (slows the target). Min maxers will under any cercumstance, if it does damage, they will tell you what the best tallent is. EX glaive toss is better single target, barrage better aoe, powershot is a PVP talent. Lynx rush was epic burst combined with BW and rabid (when it gave pet 70% more atack power or something). they nerfed it to a bleed, its now the weakest dps ability for that tier and few people use it. The issue with amp tier was 2 were dps tallents, one was a utility (a slow).
The issue, is coming up with 3 utility benifits that are tied to all our shots (mostly amo in this instance), where one does not out shine the others (see the wyvern sting, silencing shot, intimidate teir), is dificult, with out making all 3 either OP or worthless, or making them do different things.
An AMO tallent/slot/ability that does this would give us passive and constant abilities that are ranged and can not be countered with out ccing us. As is, our concussive shot has a cd, and most of our utility debuffs are tied to our pets which can be kited. melee have thee kinds of things for auto atacks (pallys, shamans) but they can be kited, other ranged dont have constant white damage that can maintain utility debuffs while they use other abilities. Giving us such an advantage would make very hard for a melee or caster to counter it. The only Utility they could give us with amo is damage components, which is why they tried that in the beta. It was determined to be to much of a dps talent, and one being only a pvp talent, so instead of having 2 tiers of damage tallents with pure PVP/single/aoe edges, they gave us the disengage tier instead.