I don't assume that at all, but what I do see is a description of Eden in Genesis 2:10-14 that could not have been made if the tectonics had changed the mountain heights as you are suggesting. And the Genesis 7:19 translation you mentioned supports my point of view anyway.
Who wrote Genesis chapter 7? It was either Noah or Shem. (Maybe Japheth or Ham recorded their own version of events for their descendants, but Moses most likely got his story from his own ancestors.) In any case, it had to be visual. A flood came, he was floating around in an ark at the mercy of God for a month and a half weathering a storm, and then after the rain stopped all you could see was water. How else are you going to record the story? "All the earth was covered, but maybe some there are some distant mountains I missed that were still were above the water."
You can argue that God wrote everything himself for Moses, but even if that was the case, it certainly wasn't detailed enough to cover everything. Otherwise, you might have seen something like "every creature that moved along the ground went into the ark, but a few went extinct, because the Mastadon's and the megafauna from North America wouldn't fit." The creation account in Genesis chapter 1 certainly isn't a complete story, and neither was it meant to be. It was simply a basic story that would be understandable to everyone who read it.
He had to have a way to get garbage off the ark. In particular human and animal feces would have had to have been cleaned up daily. Regardless of whether it was raining or not, You would have had to see outside; however briefly in order to do this. More than likely observations started happening as soon as the rain stopped. Genesis 8:6 says that Noah made at least one window on the ark.
A simple rope with knots tied at regular intervals would have been enough to tell how deep the water is, as described in Genesis 7:20. The rain stopped after 40 days, but it didn't start receding until 150 days. At this point the ark rested somewhere in the Ararat mountain range, but the tops of the mountains weren't visible for another 5 months. So is Everest already pushed up to 29,000 feet by this point or is it still pushing up a couple thousand feet per month to become visible. Or is it just possible that since it was several thousand miles away that Noah didn't see it?