Do we know exactly how Koine Greek was actually pronounced?
Yes. It sounded very much like middle and modern Greek.
It did? What about Erasmian pronunciation?
Erasmian pronunciation is for Attic Greek, not Koine. And even then I doubt whether the Erasmian pronunciation was ever used, it is 'reconstructed' in the Renaissance and it sounds plain awful.
Again there is NO SUCH THING as Erasmian pronunciation outside of weird back to the Greek Bible circles.
Go to a real classics department and run this game if you want to get laughed at.
Attic is always being reconstructed that is what philologists do.
I sat through debates (impromptu) by serious classists arguing over pronunciation of attic Greek all the time.
Erasmus developed a method. A needed one.
And you are kidding yourself if you think the Greek of today is what "Greek" sounded like even in 20 AD.
Sheesh. This should be common sense to those who have had the opportunity to experience today a language with a long history which circles much of the known world: English.
Oh how will people 2000 years from now know think I sounded if there are no recorded media left and just fragments of writing here and there?
If they come up with how Akimori sounds, well they will be far off.