I have not read the OP yet, but based on the comments this doesn’t seem to answer the full situation to technology (either land suits or some kind of underwater diving bell type of thing). Just getting crude metal smelting is not enough to fulfill the challenge of proving underwater civs. Without that at most we’ve just moved underwater civs from the stone age to the bronze age (replace with the actual metal name they can use). And to me that isn’t much of a difference, though I admit it is a one step closer (assuming the crude metal smelting can lead to proving later technologies and isn’t a dead end).