The 5DII and 50D are of a similar tech (and the 50D has the advantage of gapless microlenses) ...
If the 50D has an "advantage" then they are not completely of a "similar tech."
True...but that tech advantage favors the APS-C sensor, and the FF sensor still wins by a big margin.
In your very detailed responses, I notice you conveniently ignored the fact that DxO's measurements show that a current Canon APS-C sensor has ~1 stop more ISO noise than an 8-year old Canon FF sensor, and close to 2-stops more noise than a current Canon FF sensor. I wonder why you didn't respond to that?
But if you hold focal length and distance constant, you actually get shallower DoF with APS-C.
Huh? Using the exact same lens? Are you sure?
Yes, I'm sure. Go visit a DoF calculator (e.g., dofmaster.com), or verify it empirically as I've done.