Diamond wasn't too good, McCartney wasn't that bad, there aren't many younger singers who could sing Let Me Roll It. I've seen recent live shows and he was much better, so maybe he wasn't as warmed up as when he's touring.
I hate it when people say old performers should give up, they have enough money now, etc, it's so ignorant. A truly creative person can't curb that urge to sing/perform/etc, they carry on because they enjoy it, not because they want more money.