Penetration matters a lot vs Ost. 50 cal can rip through 222, flame HT, and flak ht, and when garrisoned can do enough damage to force a Luchs back.
Having lower penetration means you can't even force back lightly armoured half tracks.
Set-up/tear-down time is also an important consideration.
I think most people would prefer the MG42, obviously, since it's the easiest to use. Just pointing out that it isn't "strictly" superior to the 50 cal.
It is: hit the field first by a larger margin, cost less, larger arc of fire, longer burst and vet1 incendiary round over the top.
Basically the HMG.50 is only better in setup time.