Imo, the usual suspects wont have a real clue until underwater archeology starts working the old ice age coastlines approx 2-300 feet below current sea levels.
You are not alone in having that opinion. There's an undercurrent in the present dabate that is growing, that believes we don't know squat about ancient civilizations and population movements. As you noted, until we get to the old seacoast, all is just conjecture, much ado about nothing, books full of science fiction that earn PhD's for the dreamers.
This may happen quickly. I am so excited about undersea drones that can use swarm technology to map the sea bottom. We know more about Mars than we know what is below the waves. The Chinese grabbing our drone shows that we are moving ahead, and there are startups on YouTube making cheap drones. It is going to be exciting over the next few decades and a LOT of questions will be answered.