Fortunately I don't check bags very often. But Detroit seems to be the worst about treating the yellow tags with priority (and they should be one of the best airports seeing it's a major Delta hub).

I have checked bags on four trips this year. DTW/MIA and in MIA my bag was one of the first ones to be on the belt and the few before mine were also yellow tagged. Coming back to DTW, there were bags without the yellow tags off before mine but there were still people waiting after my bags came off.

DTW/MDW at MDW bags were already on the belt when I got down there so not sure how it was treated. Coming back to DTW there was over an hour wait on the bgs (we landed in C so not sure if that had anything to do with it) and my bag was the last off but only five others had a checked bag so didn't realy matter there.

DTW/MSY, at MSY my bag was one of the first off and the others off before mine were also yellow tagged. Coming back to DTW a lot of non yellow tags were on the belt before mine, but there were still others waiting on luggage when I got my bag.

This past weekend flew DTW/EWR and my bag was one of the first off and all the bags before mine were yellow tagged. Yesterday LGA/DTW there were a lot of checked bags on the flight and I had a decent wait on mine. Mine was second to the last to be unloaded and all the kettles bags came out before the yellow tags. All the bags that had yellow tags were the last to come off on the belt.

If I have to wait a couple extra minues on my bag it usually isn't a big deal and I am happy it arrived, but I agree with the OP, that if Delta is going to advertise it as a benefit, then they should enforce the policy that yellow tags get priority treatment. Whenever I check a bag back home to DTW, sometimes I am tempted to tell the agent NOT to put the yellow tag on the bag since the yellow tag in DTW seems to means I get my luggage last instead of first.