Unfortunately I didn't keep any detailed statistics of pool vs non-pool catches. I can post some totals (fish totals to be precise). I did do 3300 catches total and about 1000 of those must be pool catches. After I didn't succeed with pool catches I decided to just to open water and opportunistic pools to speed up the fishing speed considerably, and make the time commitment more TV/distractor friendly.
I didn't keep count of crates and crystalized water. But here is my fish count:
1359 Fangtooth Herring
1107 Bonescale Snappers
347 Glacial Salmon
180 Pygmy Suckerfish
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2993 fish catches mixed from open and pools. The rest of roughly 300 was crates and crystalized water. As said elsewhere, I have never gotten snappers, salmon or pygmy's from pools, but the chance for crates and crystalized water seems fairly good in pools (subjectively).
I have no clue if pools are any better than open water, because I wasn't successful with either. I think if the pool chances were significantly higher, i.e. in the 1% range I really should have seen one if not a few. If the percentage is 0.1% or lower, who knows... and if there is a 1:2 chance difference it will take a lot of catches to tease that out. Even so people have to decide then if doing two open water catches without traveling isn't faster than traveling for pools and recasting to actually hit them. Then again I may just have gotten unlucky with pools (or both). But I'm speculating.