The problem we have is that Ndombele, although regarded as a technically very good footballer, has failed over the 2 years he's been at Spurs under Poch, Mason, Mourhino and Nuno to consistently perform.
This season our core midfield has tended to be Hojbjerg ad Skipp with Ndombele usually playing a bit in front of them (and Dele in a similar role earlier in the season).
So unless Ndombele plays like Laszarus in a remarkable resurrection back to the Lyon player we thought we had bought, Kessie has been brought in to be the creative player to compete with Ndombele or possibly to play in a 3 with Hojbjerg/Skipp with Kessie and Ndombele - but if Ndombele doesn't want to exert himself Ndonbele .becomes more of a bit part player.
Remember Conte comes with a reputation of training players hard - something Ndombele seems to be allergic to.