There's a number of ways to separate categories though, and even make players ineligible from one to the other. Besides which, I don't think a player has to fit a sole category if he is skilled and replete in the body of work and performances in both. Let at it and see how good that player is, in that role, compared to the specialists, I would say. How does Neeskens (one of my favourite players of all-time) fair against a pure DM, for example? Has he even got the amount of games playing the role to contest it?The thing is, you won't be able to compile a good list of 20 DMs and 20 B2B midfielders without many overlaps and questionable inclusions/exclusions. There's going to be about 10 duplicates in both lists and it just doesn't make sense to create 2 different lists when they're going to overlap by this much. If you'll compile 2 comprehensive lists that I won't have too many objections about @Fortitude...
Or you can set a strict ruling, like we did with those categories, that certain players go to this category and certain players go to another. Which will cause even more issues on where to put Rijkaard, Keane, Voronin, Pirri etc.
I think another thing to add is that, generally, DM's facilitate others, whereas CM's do far too much to say they're there to get the best out of others, hence, when they are great, they are comic book hero level players.
For me, Keane only became a DM when his hip went and he had no choice but to sit. He was great in the role the little played it and even schooled Gerrard from there, but I'm not sure I'd categorise him in any DM list whereas he ticks all the boxes to rank comfortably top 10, and arguably top 5 at CM.
If this is something to delve into, I'm sure a cohesive and logical set of parameters can be written up, though.
Cheers, harms.