Messi is still fast that he hasn't the endurance to make a lot of sprints.
He can still make the difference in this team due to his amazing technique.
The reason why Barca do not win a lot of title isn't Messi but the problem is in other positions.
If only my messi is relied on, then I'm sure the team will not be strong in defense and still other positions need to be applied accordingly. Barcelona only relies on Messi's attack with his best tactics but I don't think that's enough to win titles and even lose many titles.
If Barcelona are still keeping it then there needs to be a change. I'm sure Koeman can do this and win again as expected.