I use my ankle knife as a tool more then a knife I jam it into sand to give me a handhold in heavy current for prying and the serrated edge is great for cutting thick rope be knifes have their place and use or they wouldn't be sold
Bingo. Is there anything else in scuba you can use as a little pry bar? A longer blade gives me a smoother pull across heavy rope as well.
But I don't like serrated blades. I use a Work Sharp sharpener to put a thinner kitchen knife edge on my blades, if they're thin enough to support it. But it doesn't last long and needs sharpening after ever few real uses. (it's only 1 minute of work)

Which is why I generally prefer cheaper rustier knifes, I'm just going to hack my own edge on them anyways, as long as they're decent spring steel, I'm GTG.
My K-bar looks silly on the belt of my ultra light backpacking setup, but everyone's always putting away their little knifes and borrowing it, so.......
OP: I make my own belt sheaths from Kydex. (knifekits.com) They're way thinner than thermomolded plastic, but may scratch up the knife. You can make any type of sheath you want.