Personally i liked the first wip, the super fast swimming, it feels better because i almost don't have nothing to do in the bottom of the ocean really. Anyways, saying a pro of the actual effect you can make a water road (1 block deep) and go super fast everywhere with the Depth Strider boots, but that function will be the same of roads right?

Pros and cons of the actual effect (my humble opinion)
Pros:

1. You can farm Squids, but no so easily (if the water is too deep. The squids swim in the middle-upper region of the body of water).

2. You can farm kelp (future Minecraft versions).

3. You can check an Ocean Temple (you won't mine very fast but you can use the sword normally).

4. The water roads, a cheaper alternative of the new roads.

5.You can defend yourself from enemies, submerging and staying there indefinitely or running and going out in a safe place.

6.Build in the water (for any purpose) without problems.

7. You can explore faster in the bottom of ravines where occasionally the waterfalls make a water platform that triggers the armor and let you explore very fast and with night vision.

Cons:

1. not very useful, the bottom of the ocean is not very interesting.

2. you can't move freely in the water, you can't jump and emerge if you are not close to blocks

(This is just a commentary, an observation, i do not want to pressure anyone or misunderstand this as an agressive thing or a needed change).

Together with the tinker it could be a good effect; We could also insert a kind of slingshot but a subaquea (Type a jump of 100 blocks)