The point of the two different classes is to make members more obligated to take part in Spartan activities. These lower nations were not forced to do tech deals, and instead were given the option to have Sparta do it for them. Second, everyone has the ability to go up to the next rank. Its just a matter of whether you are willing to put effort into your alliance or just rake the benefits.
btw, this is coming from a perioikoi, not a spartiates.