Bentancur is not as good at 6 as Bissouma, simple fact. Biss is a very tidy tackler and his ball carrying under pressure is significantly better than Bentancur's. This is very important if you are going to play out from the back, most of the teams in the league are playing a mid block these days so you need someone who isn't going to shit the bed and give the ball away cheaply in a dangerous area, and for that Biss is your man. Bentancur is a much tidier passer of the ball and has fantastic off the ball work, making himself available for passes and progressing the team in the middle 3rd of the pitch, he is not shy of a tackle but defnitely not as proficient as Bissouma. Bentancur also seems to me like he has the potential going forward to be a goalscoring 8 in the Gerrard mould, he had a good run of goalscoring form prior to his ACL and scored against United on his first proper start back (if you discount the Villa game with the early injury). Again, that's a trait that would be wasted by confining him to the 6 role.
I don't really think Biss has "shit the bed" in any sense either, he has had games where he hasn't been as good, granted, but I can't think of one performance this season that had me with my head in my hands whimpering softly in the corner as I did many a time last season watching the Skippbjerg nightmare.
