Zerk's not happy with Guards getting additional AA's

I have just rolled a zerka so have very little to say about the differences between the two classes however have a number of level 70 toons that I have betrayed both ways to experience the alternate sub-class.
While I can understand why on a first betrayal fairness dictates that you end up with no spells of consequence it seems strange that a return to your original sub-class and subsequent betrayals do not maintain the spell levels earned or purchased in the past.
If previously scribed spells were maintained this would give people the chance to experiment within their chosen class.
With the warrior class especially it would allow the game designers to strongly define the stereotype rolls, strong defensive guardian tank and axe wielding DPS zerka that can step up to the plate for lesser encounters. There is only ever going to be a limited number of spot available for a fully defensive build tank on raids and it just makes sense to me to allow those who do not fill these rolls regulaly on raids to be able to take on a better DPS roll with the option of swapping back when there is an opening to take on the MT roll.
I have a feeling this approach would provide a clear indication to the game designers where there is perceived sub-class imbalance as one sub-class would end up with many more than the other, however much of this imbalance would become irrelevant.
I am not suggesting the betrayal route should be to easy as this would just encourage sub-class changing to accommodate immediate need.