I can see him working in such system if he turns into CDM and we get either a mobile playmaker alongside him ( somebody who can do magic passes ) or true workforce box to box midfielder. You're asking what he's done today, well, he was a defensive midfielder. If you looked at today's performance of his and, say, performance against WBA there are many aspects that differ. He wasn't going forward so often which is more than understandable taking into consideration Liverpool's attack and the fact, that playing him and Carrick gives our front four less 'tracking back' to worry about. They can play risk passes and use LB / RB to provide width and don't worry that we'll get countered because the midfielders are there.
About seconded bolded, not really, just because our system is not working it doesn't mean that everybody doesn't do his job in this system. Out of many players there are, I think that Fellaini is doing his job rather fine since his comeback. To put it shortly, you'd expect all the fancy passing and creating from Mata, Rooney, Januzaj while fullbacks provide width. The first doesn't work, the latter does. In this case, there's feck all creating up front and the blame goes on Carrick / Fellaini ( while I can partially understand why blame would go on Carrick because he's done fantastic job as a deep lying playmaker last season, Fellaini is just not going to turn into a passer alike to last season's Carrick ).
I'd love to see how many times he's been dispossesed today because we can see how many passes he's failed. ( 36 out of 43 successful ) As I see it, he should pass it to Mata / Januzaj / Rooney ( who didn't bother dropping deep again leaving Carrick and Fellaini against 3 man midfield of Liverpool ) and let them create, if we get a decent playmaker to partner him then the distribution responsibility will be spread even more evenly. He can run with the ball, he's proved that against CP and WBA but for God's sake, he's not going to do that against Liverpool because they're merciless on the counters and neither Januzaj nor Mata did a lot of defensive work today, which is the purpose of this 'system'.