Ill admit I've not seen anything of Mckenna recently, so don't know what hes likes now.
But I think saying he was decent on the ball at abredeen is certainly a stretch. Its the one thing he was always severely lacking. Considering his physical attributes if he was decent on the ball he would have been playing at a much higher level much sooner.
He looked awkward in possession often, and likely to make a rash challenge or mistake even if he has plenty of time.
As mentioned previously when he came on against Croatia he looked nervous and out of his depth.
Im certainly not writing the guy off. He was also a good defender and read the game well players. Players can improve, and technique and composure is something he can develop.
I can see a future with McKenna as one of the first choice centre backs, but only if he's got better. Or gets better.