I don’t see a problem with Andrew attending, it has been reported that, as a near(ish) relative, he was invited by the bereaved family and it was a private occasion. In fairness there are several photographs of foreign royals smiling, but it appeared that they were greeting each other, frankly much as many do when they haven’t seen each other for a while.
Maybe if our Royal family had arrived in small family groups, rather than in one long one headed by Andrew, his elevation to the most senior royal there would not have been so gratifying to him, and he would not arrived beaming.
He did in fact sit in the same row as the Queen, who sat next to Princess Anne and her husband, then the Duke and Duchess of Gloucester, then Prince Andrew , followed by Marina Ogilvy who was presumably helping Princess Alexandra who was in a wheelchair. So working royals did take precedence during the ceremony.
The arrival arrangements really did seem to be a step too far. I really don’t think the same mistake will be made again.