Since Nola's return, he has had 1 middling start, 1 very good start and this really bad start.
In other words, he is searching for equilibrium post-injury and time away from pitching every five days. IMO, this is as expected for any pitcher, but especially for Nola who, as andyb noted, depends quite a bit on his command and location instead of velocity.
We'll have to see how his next couple starts go, but it would be much better for the team if he can round back into form this month and be ready for the playoffs as a starter.
I would have Sanchez as the #1, with Nola #2 and Luzardo #3. Suarez fits better in the pen since he has performed well there before and can handle the pressure.
However, again the rest of the team needs to be do their jobs i.e. the offense and pen as well. The rotation has been our strength all season which led us to fortifying the pen and lineup at the deadline. Now with Wheeler down and Nola & Walker struggling, we have rotation questions too unfortunately.