given how Lambert seems to be disregarding Bent full stop (planning to sell him I wonder?) it seems unlikely
See above.
I'd agree with your points above but theres one problem, your not scoring goals atm so why aren't you using a proven goal scorer, Bent has already proven he can play in shite teams and score
Because Bent won't do anything other than apply the finish. If you get it into the box to him, he's a good bet to put it away. What he won't do is drop back, fetch the ball, work to create chances for other players, or put in a shift elsewhere on the pitch when needed.
Right now our biggest problem is that the midfield isn't creating chances, we're not getting the ball into the forward players with enough regularity for them to score.
Benteke puts in way more of a shift than Bent does, and is doing ok (4 in 7 or 8 games so far). Weimann also works tirelessly when he gets a game.
Bent, on the other hand, will wait for the ball to come to him. Right now, we can't guarantee getting it to him with enough regularity. That's the problem with Bent, and currently it is a major issue for us.
I never think that the route to improvement is in selling your "best" players, but if Lambert were to move Bent on in January for anything like a decent fee, and invest the money in the midfield, I would totally understand why.
I wouldn't worry about the midfield too much mate, you are playing Sunderland