While I don't really understand the squared design of the downtube, I can not imagine that an average rider would feel any difference. Especially because I guess the front wheel will make the bigger difference in that area and It should kinda shield parts of the downtube from the air flow.
I think the rider position, clothing, ... will make the biggest difference in aerodynamics.
we know for a fact that rider & clothing matter more than the bike itself, it's about 80% rider and 20% bike, afaik.
That being said, a bus shaped tube is a bus shaped tube. Even without a wind tunnel, we know that tear drop / kamm tail shaped things are more aero than round things, or boxes... And we know that buses aren't aero. You wont find an aero frame with a wide, boxy shape like that, nor will you find a frame that touts its aero prowess with a boxy shape like that - until proven otherwise, ofc. Given it's an ultra light frame, and making frames of that weight at this price point is a new phenomenon, and that LC doesn't make any aero claims, i think it's safe to assume it's not aero. Whether it matters or not is subjective. But even if it "only" costs 5W at 45kmh, i try to spend my money diligently, and given how incredibly hard it is for me to raise my ftp by 5W, if i'm going to buy a frame, and if i can, i'm going to avoid buying one that screams "i'm a bus". It's a guesstimate. It's also an aesthetics consideration, as i dont find that boxy shape appealing.
