Therte are a LOT of ancient cities under the waves as the sea level was far lower during the last ice age. If we have another ice age we may re-discover and have to re-define the history of humanity.
I disagree with your concept that the seas have risen.
The land rises and falls, and very unevenly , I might add.
Water, being 'fluid', simply flows to the lowest spot (because of gravity), and maintains a very smooth/flat surface.
It is the land moving up or down that makes water appear to be rising or falling.
The 'tides' are one of the few examples of the ocean level actually rising or falling. Even in that example, the land also rises and falls with the tides.