Yes, there are many things to take into account.
Like first serve, second serve, variation, hard to read, speed, position, kick, slice, under pressure and many more ...
Something that surprise me is why Raonics serve is so hard to read, I have always thought that a slow serve-
motion makes the serve readable but that seems not to count for Raonic. (Compare with Sampras, Ivanisevic and Roddick.