Dembele was excellent defensively next to someone like Wanyama or Dier (when good). But we couldn't play him as the dedicated DM next to a more creative, less defensively aware player like we could with Sandro, Wanyama or Dier.
I'm slightly concerned that we have a similar "problem" now if Bissouma isn't there. Sarr, Bentancur (and Hojbjerg to some extent) are all very good defensively next to a DM. Pressing, working hard, getting around the pitch. We're yet to see if any of them can be the one with that DM responsibility and do it well enough imo.
Skipp can be that player in some systems (imo), but not sure he's a great fit with the requirements of the system. I think we need the DM to be rather quick, not just get around the pitch and find the right positions, but get there quickly and be an excellent tackler.