As far as I can tell, the LHT is tig welded aircraft grade 4130 tubing. It is listed as having a double butted main triangle. Perhaps not as sexy as some of the new alloys, but it is a workhorse. Nothing mentions (on the Surly site) whether it is seamless tubing throughout, or not, but that would be a minor distinction.

Trek lists the frame as using Trek 100 alpha series aluminum. As far as I can tell, it may just be 6061, which is a very common weldable alloy.

One thing that Trek is doing is using hydroformed tubing. Some of it may be just for show and to imitate CF bikes. But, I think there are specific weaknesses in bike frames including the bottom bracket. Hydroforming allows shaping the tubes (and hopefully also tubing thicknesses) for optimum strength. At least in theory. Whereas the LHT has more of a traditional shape.

I've heard of frame failures with all materials, steel, aluminum, titanium, and carbon fiber. I couldn't say that any one material is particularly superior than another. But, perhaps it comes down to construction techniques.

The typical aluminum frame is much lighter than a typical high-ten steel frame. However, the differences are small when comparing to butted chromoly.

Perhaps one should look at one's intended riding. I use my Colnago Super for light to moderate on-road touring.

I'm wondering if the LHT and the 920 are speced for off-road riding. Build the frames for the worst conditions that they will encounter which makes sense from an engineering and warranty perspective. But, if your target is basic on-road riding, they are likely over-built.