Height and weight are the easy part. The rest is temperament, and it is the reason we ask about your worst ride.
The form asks for your height, your weight and how long you have ridden. The conversation at the mounting block asks something else: what went wrong the last time, and what you did about it.
A rider who freezes needs a horse that does not read hesitation as an invitation. A rider who overrides needs one that ignores a loud leg. Matching on size alone produces a safe pairing that teaches nobody anything.