Considering Diego had most of Colombia up his nose and was still better than anyone, I think Messi is miles ahead. It was a different era but plenty back then scored a shit tonne. Tackling was tougher, pitches were shite but fitness these days makes it so much harder to stay at the top of your game. You could be naturally gifted, turn up half cut and still be miles better than anyone back then. These days you have to do so much more to become successful. Plenty of people with natural talent have done fuck all.
I get what you're saying about Argentina's world cup campaign but that's more evidence that Messi is the greatest. He's been through disappointment after disappointment with Argentina, in much better teams too. But he came back fighting, won the Copa America being the best player and has now added the World Cup. Turns out if you get a squad that works for him and with him, you win things! He scored in the group and every knockout stage. He's undoubtedly the best ever. Maradona doesn't come close, he was just a cult hero who on his day was exceptional. But he had plenty of poor games, doesn't have a record anywhere near as good, and as I said at the start - he liked his drugs.