Nola has had this problem for a while.
When he's on he can be untouchable, but he also has a thin margin for error. When he's "on," the two seamer has movement and hits the edges, the 4 seamer at the top of the zone, the curve drops out of the K zone, the change up fades down and away from LH hitters and so on.
What I see when he gets tired isn't a big drop in velocity, but a loss of his elite command, pitches start drifting over the plate and boom. A 92 MPH FB in the sweet zone is going to get creamed.
The problem is simply that he doesn't have elite stuff, so the key to his success is command, and fatigue kills command.
That means he has to handled carefully, he's not a workhorse and they have to make sure he skips a day a times during the season, doesn't run up pitch counts, etc., to keep him effective.
And that's why I wouldn't overpay him, and I think the Phillies see the same things and that explains why the two parties were so far apart. Nola's people negotiated on the basis of his past production, the Phillies negotiated on the basis of perceived limitations.
