Gerrard is fine if we need a roving player.. Thing is we haven't that rock in the heart of midfield.. As you rightly point out top clubs have that type of player.. Explains then in part why they're a top club.
If Rodgers modelling LFC on a Barca type system then he should also know that Barca do indeed have that rock in the heart of midfield.. We've not had that since Mascherano left us.. Lucas isn't capable of doing that role as he's not that type of player..
Again it's square peg / round hole.. So get in the right players then the system will work..