"My main complaint with the Carbon Reflex 2 is that the tent sides tend to lift off the ground, especially in the middle, making the tent smaller than it could be."
Yeah this occurs because the carbon cross strut is so stiff. If it flexed easier then it would bend down instead of pulling the floor up. The aluminum poles used in the Hubba tents seem to have more flex so you don't really get this problem.
I imagine you could alleviate the problem by using a different cross strut. For example, you could easily make one using Easton Nanolight tubing (QuestOutfitters.com) or thinner carbon tubing (Fibraplex.com). The cost would be minimal (~$20) and you should net a few extra inches of floor width in the middle of the tent. With enough flex, the tent could be 46" wide the whole way instead of lifting up in the middle to 40-42".
Another solution that's even cheaper is simply to sew a couple extra stake out points to the tent in the center.
"I'd say it's more than superficial similarity to the TT Rainbow.
The main difference between the pole design of the Carbon Reflex tents and the Rainbow line is the length of the cross strut. This might sound minor, but TT uses a short cross strut to give the tent a bit more headroom. In both the Rainbow and Double Rainbow the cross strut is ~18", so you still have side walls that are sloping inward. With the MSR tents, they are using a wider cross strut that is as wide or even wider than the floor so the side walls of the inner tent are vertical or even sloping outward a little. Accordingly, it makes a much bigger difference in headroom. The CR2 uses a 50" wide cross strut in a tent that is only 40-46" wide, so you end up with a tent that is actually wider inside at top then it is at the bottom. I'm not saying the designs are very similar….they are, but there is some difference in the design.