Subject to the condiitions of each section of raceway, you do not have to run #10 all the way. You can use whatever the smallest size is that has an ampacity of 20A or greater after ambient and derating adjustments are applied.
The reality of it has some contractors pulling and I remember that some electricians have no idea about derating and have seen and been instructed to pull 72 #10s plus a ground into a #2 pipe. I had to use the hydraulic lift to complete my mission and trashed a nice rope. When I am working for another foreman in the same shop I try to give him the respect of following his direction to the best of my ability. Right or wronng it is his responsibility for the outcome of the job. If something is an IMMEDIATE DANGER I will get involved in the losing battle to protect the unknowing. It is the contractors responsibility to hire competent supervision and when they dont I take a hands off position. It is not my problem. This is the problem with not having Statewide licencing. Noone could fault you from not going along with a gross negligence situation but here the contractor wants to just finish the job asap and let the insurance carrier cover any mistakes.
Sounds like you had need to vent a little
