I don't think I've ever had to wait hours to reach a DL employee over the phone, even when I was a general Skymiles member during IRROPS.
I've only been PM a few months and have never been Diamond, but Plat has been great thus far. Of the 7 non-paid FC segments I've flown this year, I've been UG'd on 6 of them and all at the 5-day PM window. I guess being a Diamond would have gotten me that coveted LAS-SEA FC upgrade that I missed...