Shawn Peterson, I've gone through my share of heavy rains, in fact at times I have actively sought out heavy rains to go backpacking, since nobody else goes during those times, which is also by the way why I wouldn't think for a second to use a floorless tarp in any situation where heavy weather is likely.
You've already found what a bathtub floor does, trust your experience, I trust mine, I would never head out in cold weather in winter where there may be limited site selection which exclude the luxury of finding the perfect spot where water will not pool without a real tent with a real floor. Not so easy to do when the rain is driving and it's near freezing and you just want to get that tent up as quickly as possible. I'd use a tarp with net screen in certain climates I think, just not real rain situations.
Tarp tent type tents with built in bathtub floors cover a very wide range, for example, you can have Zpacks build you a large hexamid with a built in bathtub floor, almost all tarptents use a built in bathtub floor, and the trekking pole supported ones weigh only about a pound and a half, that's 1.5 pounds less than your copper spur 2 if I read it right. I believe the main obstacle you'd hit is the zpoles, most trekking pole supported tents should have some adjustment in the trekking poles to tension things, though maybe not all need that, I don't know.
Every time I look at serious rain areas like Northern Europe, and look at the tents they are making, I see basically some type of double walled tunnel tent, for very good reason, sitting in a typical mesh edged tarptent in driving cold rain strikes me as a fairly miserable way to hunker down in cold rainy climates, but each to their own I guess.