There is some kind of difference between building and buying troops with $$$$ :D.
As i said before, you simply should have been waiting until you could find out about what is going to happen (now!^^). They announced that they will let us know about 48h before the new system will launch, so buying units after you found out what is going to happen does not sound like a problem to me and yea, there are way more units than gunners to come, maybe they release some of those tomorrow... another point to concider ;D.
It´s still a very heavy defence, but i think the combination of different units is going to be more important in the end, we´ll see, but i wouldn´t say that they are worthless.^^