Unfortunately, that hasn't been the case. The shop I'm familiar with has seen much more Mesa sales since they became the only store in town carrying them. When GC has a wall full, that will unfortunately divide the small pie in any given city.
That being said, it might be a good move for Mesa. However, given the delivery delays posted here, it doesn't seem like they have massive excess capacity to fill a much bigger distribution network. So, that, and the nightmare they seemed to have the GC previously seems to make this a strange business move to me, unless they are going to overseas production on some stuff (which I would doubt).
It might be because of the fall on sales on expensive amps like Mesa. I haven't seen any Mesas move in my store since January I believe...