Not really. The player who scored was not a striker like you said, he was the central midfielder. That's not a matter of opinion.
Also not a matter of opinion, is who was marking him. If you watch the replay again you'll see Darmian is marking a different man, their RW, but when Dendoncker waltzes past Fellaini (who was the man supposed to be marking him) he has to try and come across. Dendoncker had both the better run and is taller than Darmian.
It was a very good cross and a brilliant header, but if you really want to assign blame for the goal, then that blame lies squarely with Fellaini not with Darmian. Again, opinion doesn't even come into this, that's simple observation.
Darmian was good today. Whether he's good enough to be here long term is another matter, perhaps not. And that, is an opinion