I, and I think Lorenzoid as well, are talking about dives in relatively benign conditions when you have the luxury of courtesy. Boarding under challanging conditions are of necessity handled differently.Ladders (and lifts).
Other than when you have a student, or an inexperienced buddy. The general rule is; first to the ladder; first up.
This is based on safety and practicality.
Being under a ladder on a pitching boat is not a safe place to be, so no dilly dallying, get out ASAP.
It also means the exit point is made vacant as soon as practical for other divers. Minimising congestion.
Exit and entry points are dangerous areas. Keep them clear.
(I still have the dent in my skull from a cylinder (and diver) that landed on me.)
But either way, no one should be hanging beneath the ladder before boarding and that is not what we are talking about.