Both Messi's and Ronaldo's last stints were underwhelming because they are well past their prime. They are in their late thirties, and they started their professional first team career at extremely young ages (15/16). It's a testament to modern medical science that they are still not retired. Most professional striker/midfield players either retire by 32/33 or drop deep, or go to US/Middle east for a good pay day that isn't very physically demanding. The other players who started playing along with them retired years ago or moved to less demanding leagues (Rooney, Fabregas, Van persie, Robben all retired years ago. Even iniesta who started years after these, is in Japan for the last few years). Ronaldo didn't help at all acting like a primadonna instead of showing age and leadership in his second stint at MU, but that is him.