Swimming Mob Move Speed mostly effecting y and turn speed?

I've had this problem too. However; there is a solution. Don't use swimming entity; use flying entity. Then you can make it detect air above it and move it down or up, depending on where the air is, and setting it to flying fixes the x and z. if you need it to spawn underwater, make a structure with the entity that only spawns in water, don't use the spawning option in mcreator.