So-- there are caveats. A lot of deep sea life are able to see, and it's because deep sea life also generates their own light. It's a way to communicate to mates, and a way to notice prey, and a way to bait smaller predators.

I also think that echolocation has potential to be equal or better to eyesight! Bats and dolphins do great with it, and I think that it's easy to think of echolocation as being a _visual_ stimuli, even though it's not lightwave-based.

I think the biggest hurdle for an underwater sentient species trying to become more advanced is the difficulties with tool-building. Simple stone tools could be made, but it becomes a lot harder to smelt iron and start doing metal-working.