I watched portions of a livestream last week and the framerate would definitely become abysmal in some points, but it seems to be mostly a problem at the school and big cities. It is still absurd they greenlit this, but I seems is something you won't have to deal with when you are on the field exploring (which should be most of the gameplay).
Still, funny to think that we know about this problem and how bad it was for one month already, when the early reviewers mentioned how terrible the performance was, and yet the very fanbase tried to shut the complaints by making up a completely baseless excuse of "they didn't got the final version, it was an old build of the game". The Nintendo Life reviewer dedicated a huge portion of his video
to detail the performance problems, but instead of making a huge deal of it, we made up a complete lie to cover it.
When the fanbase tries to shut its own complaints, it's no surprise GF doesn't have to worry about poorly finished product - they won't even have to make excuses for themselves, just trust the fanbase to make those for them.