It depends on what should be the physics of the game, but you're comparing apples with oranges. Jumping/falling can't be constant because of the climax of a jump (between 1 and 2 blocks).

In addition, no velocity is lost when falling down 1 block because of logical terrain movement.

ughh fine try moving forward on flat terrain and then jump, you should hear the fall sound. Then try jumping onto a 1 block ledge, where you won't hear the fall sound and also not lose speed.

Edit: and I just tested this to be sure, when you land after jumping 2 spaces, you do in fact slow down slightly as compared to just jumping one block.

well ur in water

whenever you fall 2 blocks or more you slow down, even if by a little. You can tell by the falling down sound that is played (sounds like equipment falling). You can test it easily by jumping in water while moving forward, you will notice after the 2nd or 3rd jump in a row you will be almost not moving at all.

What slowdown are you talking about? I have had no issues with it since the update to 2 blokc jumps.

Make it so that when you fall down 2 blocks you don't slow down.

Reasoning: Before the change from 1 block jumping to 2 block jumping, jumping never slowed you down. Now whenever you jump, since you are moving up 2 blocks instead of 1, you will always slow down when you land. So raise the trigger for slowdown from 2 to 3 blocks.