I had almost exactly the same experience. My upgrade percentage was dropping below 50% on Continental, with the added frustration that all the routes I fly were being booked to capacity. There were times I want to come home early, and it was _impossible_ on Continental.

I sent in a Status match request to Delta in March, was upgraded to Gold Medallion within 24 hours. I proceeded to book out my next 3 months travel with Delta.

I have not missed an upgrade yet on a Delta transcon on my primary routes, and that is flying as a Gold.
Thanks to Delta doing a Double MQM promotion, I just made Platinum (3 months from 0 to Plat). I expect my upgrade percentage to go from ~80% to close to 100%.

Continental's airplanes are too small and too full. As far as perceived quality, CO has nothing on DL.