Okay, I just did a check on the 7-game winning run and the Jorginho-Kovacic-Mount trio was played only twice, in the last two wins of that run - 1-0 at Ajax and 4-2 at Burnley. In fact, if we take it a little further, that midfield combination only started 4 times when we had the run of 9 wins in 11 games - the last of which came in the debacle/crazy/great 4-4 game against Ajax.
W 7-1 Grimsby - Gilmour/Barkley/Pedro
W 2-0 Brighton - Jorginho/Barkley/Mount
W 2-1 Lille - Jorginho/Kante [back 3 was used]
W 4-1 Southampton - Jorginho/Kante/Mount
W 1-0 Newcastle - Jorginho/Barkley/Mount [Barkley was subbed off with injury for Kovacic before HT]
W 1-0 Ajax - Jorginho/Kovacic/Mount
W 4-2 Burnley - Jorginho/Kovacic/Mount
L 1-2 Man United - Jorginho/Kovacic/Gilmour
W 2-1 Watford - Jorginho/Kovacic/Mount
D 4-4 Ajax - Jorginho/Kovacic/Mount
W 2-0 Palace - Kovacic/Kante/Mount
So, is breaking up the Jorginho/Kovacic/Mount trio really the issue here? It's highly debatable, because we have experienced this trend before - start the season well and then things go off the rails around November-December. I don't necessarily disagree that Kante looks something of a misfit at times in the style of football we're trying to implement but the bigger issue here is a lot of the players have suffered a dip in form at the same (wrong) time. And if the results above are anything to go by, it seems our poor run of form started when Mount (and arguably Jorginho as well) went off the boil because he's the one constant in the run above.