In some expansions (including my WOTLK client from 2009) and in the 1.12 client:
If I have altered my swimming direction by holding RMB to go down or up, jumping out of water then swimming forward again resets that direction and makes me swim in a straight line parallel to the surface of water.
On ground before reaching the water: If I am running while holding RMB towards the ground like most players who don’t use keys to rotate, then I release it before jumping into the water, same thing, I will swim in a straight line parallel to the surface instead of down.
While swimming up: upon reaching the surface with RMB and no jumping, I will swim in a straight line again, parallel to the surface.
In Classic & BFA: my RMB camera affects the direction towards which I will be swimming both before AND after jumping out of the water.
On ground before reaching the water: holding RMB towards the ground and releasing it before jumping into the water will make me swim down instead of a straight line parallel to the surface.
While swimming up: if I swim almost straight up and reach the surface, I will move at like 1% speed or not even move at all and my character will swim on the same spot, perpendicular to the surface of the water.
Also, on the 1.12 client, using the sit button to swim down does nothing, and I can jump underwater. So Classic/BFA is better in that aspect, but the direction not resetting is very annoying. What it means is that once I alter the direction, I cannot reach 100% of my speed in a straight line again without additional mouse movements. Indeed, the direction DOES reset but only when the camera angle is very close to water and almost parallel to the surface.
This is annoying for any swimming in general but also when fleeing from a monster or player and jumping into the water, because it will make me swim down instead of straight forward and waste distance until I manually move my camera very close to the water and waste a lot of field of view. And this isn’t BFA, I cannot fly or walk over all the water I encounter. You can try it yourself in ponds in the Nelf starting zone.
I am not asking whether it is immersive and I should get good. This is not a First Person Shooter. I am asking if it was like this back then or if this is like I think some BFA mechanic left over to accommodate the retailfrogs.