this one comes the closest to the CruX in terms of geometry, and has one of the lowest weights for a gravel frame you can find as well. Despite the fact that the evidence is clear--with 2 independent reviewers confirming--that this is a bike that "feels slow", I have a hard time wrapping my mind around how that can be.
@GratiotGravel, are you running the same tires between bikes when making your speed/watts comparison?
Are both of you running big tires, generally speaking?
About the geometry (comparing Crux 56 vs LCG071 55), I'd say they are quite different if you're talking about the latest edition of the Crux. Save from the (probably) more complicated carbon layup the Crux also has 1.) 5mm shorter chain stays compared to the LCG071 which would contribute a lot to the perceived "sluggishness" of said bike in my experience. 2.) the Crux has 11mm longer reach which comes closer to a road bike which alters your position to become more aero and aggressive as well as giving your legs some more leverage. 3.) 20,6mm lower stack which could contribute to it feeling a bit more nimble out of saddle.
So summing it all up I think there are quite a few logical reasons for them being quite different bikes. And about the tire size I run the Vittoria Terreno Dry 38/40c tyres on all gravel bikes I test with a set of light Farsport wheels.
I'd look for a gravel bike with as short chain stays as possible where you can run your tires of choice combined with a rather long reach and fairly low stack. The Twitter Gravel V3 has really good geo but unfortunately does look a bit messy inside so can't vouch for the quality, runs great though, very responsive and fun ride. I haven't yet tried the Airwolf YFR068 but that looks quite interesting too (same chain stay length as the Open UP which has a really responsive rear albeit tends to loose grip a bit for various reasons).
Hope that's helpful