If you don't trust the shop, you shouldn't let them do the build. You can probably get someone here to say one thing or another, but they have the details, and have met you. That should do it.
While 180 is a totally normal weight, it is upper end for competition tubing. There really isn't any upside to shaving tenths of a cm on a touring bike tubing wall. I don't even prefer a butted tube myself, but that certainly puts me in the outhouse as far as the majority is concerned. For every 1/10 of an mm of wall on a 24 inch tube you are saving 1/2 ounce ish.
A loaded touring frame really needs heavy walled tubing so it doesn’t sway around (particularly the back end) when climbing. I would never choose Spirit for Lugs for a touring frame because in my opinion it is way too light when the panniers are full. That choice would be a mistake. Depending on much stuff you want to carry I’d even put a in 1.0/.7/1.0 OS down tube. It is also important to not put light chain stays and seat stays or fork blades as well. I remember a touring frame I made for myself back in the 70’s with the heaviest tubing Reynolds made at the time (of course it was with standard sized tubing) and was really disappointed with how it handled when fully loaded. When I built another frame for myself using Columbus SP that had heavier walls in the back end the ride was much better. Both the Reynolds and Columbus had 1/7/1 main tubes.