Forget about it.
There is no good reason for you to point out to your friend who've already spent nonrefundable money as to why they wasted the moneys.
Heck, I see friends hire other pros all the time, with interesting results. Should I tell them they should have hired me? They knew me, they know i do photography , and yet they hired a wedding pro who put 3 photographers to block the view of all the wedding guests by standing in a half circle around the bride and groom around the altar. *sigh*
Well, as long as they are happy
.