I had a bud (real story, I was there) who went to a guy from the SF group on post to put a scope on his hunting rifle. He couldn't figure out why he couldn't get it sighted in. The SF guy had mounted it sideways. Just because someone is SF, Ranger, DELTA, Boy Scouts, or a SEAL doesn't mean they are a weapons expert. Yes, some are the finest in the world, but not all. There are also medics, commo, intel, log, engineer, and many other fields in that world.
If hes with CAG (Delta) and graduated the operators training course he is an expert and hes extremely proficient with a wide variety of weapons.
Ive seen very few operators that couldnt smoke most civilian instructors on both knowledge of mms and skills with handling of a weapon.
To be clear their end game is not to put tight little holes in paper while standing on a firing line. Their end game is CQB and they clear rooms in low light / no light while moving around innocent people. So in this case I would take advice from any CAG operator.
Your end point about medics/commo/engineers/Intel makes me wonder if you have ever been around the SF community - Who do you think makes up an ODA?? (12 man team) their are only two light weapons guys on the team .
I think the problem your pointing out is the difference between the support guys and the operational guys. NO SF guy mounted a scope sideways. It may have been a support guy asigned to an SF Group but not an SF guy. Same goes for the SEAL team members and the guys in the ranger bats
And yes even among the teams there are some elements that get more training with certain weapons but by and large in the SPECOPS community the team guys are well qualified to give advice on small arms.
here is a video for your viewing pleasure