The Piano room is some 300 feet from the entrance to the cave, and you cannot see daylight from there, even in the very best conditions. And at it's deepest it's 110'.
So it's a cave by distance, by light, and by depth.
However... even the most egregious rototiller can't silt it out to the point that you can't see your way to the pipeline, and the pipeline going uphill goes out. The main passage isn't exactly straight, but it's straight enough that you couldn't confuse it with a side passage (did I mention the pipe?). So while I object to OW divers going to the piano room, and I don't allow any of mine to do it, thousands do go there every year... thousands, and without mishap.
So, like I say, as caves go, Vortex to the piano room is probably the safest cave on the planet.
Rick