That's right, I agree with you who say that star players can really make a difference but not only Messi because just like Ronaldo who managed to lead Al Nassr to win the Arab Champions League because the two goals were all thanks to Ronaldo.
Now star players are one of the mainstays of every football club, even though it is true that star players like that will not create a team, but when in one club there are star players, there will be an advantage in every match that is played.
It's not always Messi and Ronaldo, but there are so many star players out there.
Mbappe, Neymar, Haaland, Osimhen, Leao, Lautaro Martinez, Vinicius, Lewandowski, Bellingham, Saka, etc etc, if they're not playing and you don't see they name in the line up, they're not heavy favorite.
Remember odds are greatly influenced by bettors, most of people judge the performance based on the line up.