Even boiling it down to just original non-sports series (in other words, excluding Sunday Night Football), NBC was absolutely dominating the landscape through the end of The Voice's fall season in week 13 (the vertical line). CBS and ABC were very close in the race for second, and Fox had fallen into fourth place despite having the strongest series in Empire, with significant problems on almost every night other than Wednesday.
The Voice's hiatus has clearly been a bad thing for NBC as well as ABC, which has also had many of its heavy hitters on hiatus. CBS has picked up a lot of steam largely airing the same lineup it did through the fall, just getting a nice relative bounce due to higher viewing levels and its opponents' weakness. And Fox has been in the rather unique position of picking up a ton of ground while its biggest series is off the air. Though no Empire has hurt Wednesday, The X-Files and American Idol (and even smaller-scale players like MasterChef Junior and Lucifer) have made the overall schedule stronger.
It feels like NBC has weathered The Voice's hiatus better this year, with Chicago Med fueling huge improvements on Tuesday, plus very healthy Wednesday dramas and decent newbie performers Superstore and Shades of Blue. However, the lack of Celebrity Apprentice and no Super Bowl bump for The Blacklist cancels out most to all of that. The network actually lost about as much ground this year as last year during the Voice hiatus; here's the chart for the same period last year.
Can Fox remain a factor down the stretch? Last year, the network continued growing through the end of Empire's season, then ended up giving back those gains after it was over to end up in virtually the same position as when The Voice returned. This year, unlike last year, the network is actually gonna have Empire in April and May. However, overall the schedule may basically revert to its fall form; The X-Files is over, and American Idol has only a little over a month left. I kinda doubt they'll be there at the very end, but we'll see!