I didn't use Wikipedia as my source. The latest data was posted this year on PBS Eons.
We have never did archeological digs in 200 to 300 feet of seawater. And evidence of such town and settlements point to them being now under water. Just look at that city they discovered of the coast of India. And the megaliths off the coast of Japan. If you want to find them then you will need diving gear.
The thing is, we don't
need Archeological digs under 2-300 feet of seawater. We need
any evidence whatsoever. If a theory requires that a wide-spread technological civilization existed
exclusively within areas that are now extremely difficult or impossible to excavate, that alone makes the theory suspect. Not disproven, but suspect.
If a post-industrial civilization was large and prosperous, we would see artifacts from its existence in other parts of the world, even if it was just a handful here and there. There was and is trash created by modern civilizations, in places where native tribes still live at a stone-age level.
Beyond
that there's the issue of the ocean floor. Ships. Now, when you're close enough to islands and continents, you have steadily-building layers of mud, silt, and sediment. When you get out into the open ocean, you have a lot of exposed stone seafloor. Some of it's way too deep to explore expediently, but some of it has been explored nonetheless.
And do you know what we've found absolutely none of? Shipwrecks from a pre-impact civilization.
'The primary sites are places we haven't looked yet' is not a
completely unreasonable position to hold. 'No signs or relics whatsoever have been found anywhere else in the world at all'
does make the position unreasonable.
As I said before, a sophisticated civilization existing like Rome or ancient China, pre-impact? That's plausible.
A large industrialized society? That's not plausible.
Not impossible, there's a sliver of a chance, but there isn't evidence to support it, meaning it's nothing but unsupported supposition.