I'm not in the best position to give advice; I admit I have this problem too!
But there's no need to get rid of your tent just yet. For one, UL backpacking is here to stay and technology usually doesn't go backwards. That is, you can wait a few years, and the SUL tent you buy in the future will be as good or better than the ones available today. Ultralight hiking is a sort of backward movement, though, if you look at where gear makers have taken things.
Also, 3lbs is pretty light already, and you'll probably sleep pretty comfortably in that Big Agnes. It doesn't require wonky trekking poles, either. You say you're new to BPL, so perhaps you could save 2lbs elsewhere, without spending $200+?
On the other hand, I just swapped backpacks plus $40 to save 2lbs... so if you think upgrading(?) the tent will make you a lot happier, do it!