I wouldn't say that the Rainbow is any more weather resistant than the Contrail, given the pitch options of the Contrail (see Franco's masterworks) possibly it's the other way around. I haven't used the Rainbow but I've seen some fairly egregious weather conditions in my Contrail, including but not limited to: 40+ mph sustained winds (fun to pitch tents in), dime-sized hail, 48 hours of constant rain (ranging from drizzle to wind-driven), and a cascade of heat seeking pine cones (courtesy of Shenandoah National Park). My version is the '07, which is before Henry Shires redesigned the canopy to pitch tighter, easier.
While the Rainbow probably looks more like what you're used to in a tent considering you're coming from a BA Seedhouse, I wouldn't sweat this. Pitched correctly, the Contrail can handle any weather you're likely to be out in. The only weather conditions I would consider the Rainbow to be better suited for is a good amount of snow.