As someone who's played all roles in this story (candidate, interviewer, hiring manager, person designing the process) I'm going to argue that symmetry is more important than length.

By symmetry, I mean that at any point in the process, you and the company have invested the same amount and learned the same amount. If you're going to give me 5 interviews where I'm answering 90% or 100% of the questions, go away. If you're going to give me 5 interviews, where the first one is the hiring manager mostly telling me about the company and the role, the middle two or three are about 75% me answering, and the last one or two are mostly me getting to know some people I'm going to work with, that does seem long, but at least it's balanced. This is a big decision for the candidate as well, so presumably if the process is fair both the candidate and the company should want a process of the same length