The thing is it will be very predictable as he will counter very thing Clemont throws at him with just Pikachu I bet with his other two Pokemon being the fall guys. Plus what's the point of Clemont NOW training if he won't get his shining moment against Ash.Isn't it about how Ash will win? How'll he counter Electric Terrain? Heliolisk's speed? Bunnelby's new move? Also, what will Clemont's flaws in this battle be? And last but not least...How will Ash find it?
It's pretty much the gist of every gym battle episode(although I bet Ash will struggle most against the Fairy and Psychic Gym leaders, especially Fairy)
Again, you said the exact same thing about Ramos, and Pikachu didn't even take part. I've already told you several times that assuming is not a good thing, yet you keep on doing so.
And also, your idea doesn't really work. There'd be no point for Clemont to win AND then have Ash wait until three gym battles later to challenge him again because....well, that's not the point. Clemont is the fifth gym leader and it wouldn't make sense to move away from that order.