Might want to take a look at this thread...
https://zeldadungeon.net/forum/threads/timeline-continuity-in-botw.59056/
Both of the past two points have already been discussed there.
BotW introduces three more appearances of Ganon into whatever timeline it falls in alone... there could have been many more before that which haven't been depicted in a game (yet), so that quote is irrelevant to working out the timeline placement.
Just because a hero didn't appear before the Great Flood does not mean there wasn't one... there was a Zelda at that time, and Hylia's sacrifice made it so that there would be both she and her chosen hero would be reborn whenever Hyrule was in danger, so it's safe to assume that there was a Link...