Joined: Aug 2009
Posts: 6,722
Likes: 5,346
From: Minneapolis
Bikes: 2022 Salsa Beargrease Carbon Deore 11, 2020 Salsa Warbird GRX 600, 2020 Canyon Ultimate CF SLX disc 9.0 Di2, 2020 Catrike Eola, 2016 Masi cxgr, 2011, Felt F3 Ltd, 2010 Trek 2.1, 2009 KHS Flite 220
It's material and it's geometry - both.
You seem to be headed in the direction of one of the "plush" road bikes such as a Specialized Roubaix or the (new) Trek Domane. THese are carbon bikes. If you want to compare directly the influence of geometry vs. frame material, you can test-ride a Specialized Secteur, which is Al-framed, but has the relaxed Roubaix geometry.
I'm pretty sure there are steel-framed touring bikes that are lighter than the Surly, but I don't know too much about them.