Maddux does a pretty good job of keeping relatively upright - especially his head. Yes, he does have a slight tilt (both spine and shoulders). I don’t know if you’ll find many who are perfectly upright. As long as you are pretty close, I think that is sufficient. I think Maddux is a good example of one who stays relatively upright.
Some will argue that tilting is a good thing because it lets you raise your release point to throw on a downward plane. But it’s really a trade-off. While there may be some benefit to downward plane, raising the release point it pulls it back which gives batters more time to see and react to the ball and it makes it harder to get over the top of he ball to put curveball spin on it. Tilting can lead to early shoulder rotation and reduced hip and shoulder separation, it directs energy away from the direction you’re trying to throw the ball and it puts more stress on the arm (per an ASMI study). I personally feel the disadvantages of tilting outweigh any advantages.
If you can keep your head upright through ball release, you’re probably in pretty good shape.