Pep said to Neville in their recent interview, what is a plan b? It's small details to a game, you need to defend bring on a defender, you need to an equalizer bring on an attack, need to control the game bring on a midfielder, you need pace bring on a fast winger. I think it's wrong to assume he doesn't have a plan b, when he's won a lot of games by switching it up, he beat Spurs comfortably twice by conceding possession (they had 50% around in both games in the league against them).
Plan B has just as much of a chance on flopping matter of fact I've seen plan B fail more, Pep used it against Liverpool lol he played 4 ATB with 3 CB and a midfielder in the winger position in the first leg, which was his pragmatic approach and got punished for it.
In football their are 2 basic approach either you take initiative or you punish those who take initiative, Pep, Sarri, Tuchel are type who take initiative, while Klopp, Conte, Mou and the current RM don't take initiative. It's the reason why you lot all struggle in the league, when the team gives them the ball they don't know what to do with it.
Klopp record against Conte 1-2-1, against Mou 0-3-1 and against Pep 4-1-1.
Against Pep Klopp plays over to top to take advantage of his high line, he can't do that against Mou or Conte as they focus on defense, however neither Conte or Mou are good with the offensive side to their games, hence why they call cancel each other out at the end. Even in the CL Klopp faced more attacking oriented teams then defensive ones.
In terms of league as a long as a big screw up doesn't happen Pep should have that in the bag, as I see neither Mou/Klopp actually challenging him as they will be dealt with the smaller teams, as they have been these past 2-3 seasons, which their plan b has been nowhere to deal with them. Your right Pep issue will be teams like Klopp in CL at the end and he needs to find away around that if he wants to taste CL glory again, but he'll still have domestic glory at the end of the day or maybe he'll avoid those teams in the CL.