Your players are of high enough quality to win the league, end of story.
No Pep would not win the league this year because they're mentally a shambles, and already too far behind. But he might win it next year or the year after. I'm pretty sure Mourinho won't, even with a lot more investment. He's already peaked last year with this team, that's how he rolls, time and again through his career.
Pep signed Mahrez, a proven EPL performer, he comes in and does a job. Mourinho signs Sanchez, a proven EPL performer, he's on the bench and a shadow of his former self. Perfect example of the gulf in class between Mourinho and Pep right now.