My view on the 6 is that there is the player profile and there is the role. In my opinion, a pre-injury Bents was a perfect 6 in Conte's system. He constantly protected the back four and, if there was an exposure at the back, he ate up the ground and dealt with those holes. He also had the touch and passing to do some deep lying playmaking as well. Before that, we had all seen teams pass around Hojbjerg who didn't have the mobility to play the role. Then when I think back to the season before Bissouma joined and I remember him having 3 MOTM's against us for Brighton that season, even though they lost to us in the cup. In the 2 league games he just put the deep lying Kane in his pocket and let him out at the end of the game. He also dealt with his own marker as well.
I still struggle to understand what Ange wants from his 6. He seems to want them to play on the high press, also be box-to-box whilst covering gaps for the roving full-backs. It could easily be argued that Ange's 6 is setup for failure regardless of which player you bring in. Contrary to that thought process, perhaps he's waiting for his players to switch roles and have 3 or 4 number 6's in thought process. Then we would start to see Bissouma on the end of crosses and Madds dropping in to protect the back line. Right now, Biss would be running back past Madds on his way back. Madds doesn't think like prime Dele and just do that water carrying work so willingly. Son is probably the worst in the team for switching on defensively. He's always had that about him and I doubt it will change now.