Last game didn't really change how I feel about Warren/Harris.
Warren does great stuff working outside the tackles, on third downs, and so on. Keep giving him work there. I don't think Harris is incompetent there or anything, but you don't want to pile everything on one guy.
For Warren to really eat into Harris' workload he needs to either
a) Show he can run just as well between the tackles, into the heavy traffic, do all that tone setting, attritional stuff that Tomlin loves so much
or
b) Somehow persuade Tomlin they shouldn't be doing that so much and should be running the sort of offence where it makes more sense to give him early down work.
And for all that this offence is looking best when they lean on Pickett right now, good luck with B and maybe that's how it should be. You don't want to super lean on Pickett if you can help it until he demands it.
As for A... I just don't think I've seen Warren do that well. When Harris got hurt, iirc, they gave all that stuff to Benny Snell. Now, you can question how well Harris does it with some validity. You can question whether he should have invested in a RB rather than the OL in terms of trying to do that. But I don't think any of that makes Warren the answer that starts eating Harris' workload in the ground n' pound game.
And maybe I'm wrong, but until I see it, I won't be expecting it.