I hope nobody questions the fact of the spherical Earth. Just as spherical as all other celestial bodies.
Many argued whether we knew this fact or not, but I don't recall that those who claim we always knew also provide a reason for the Earth to be spherical.
The spherical Earth complicates a lot of things Halachicly and shatters commonly accepted ancient worldviews:
There's no absolute up and down, there's no physical Heaven and Hell, so the very idea of G-d being "up in Heaven" or "coming down to Earth" can not be literal anymore.
There's no absolute time, suddenly G-d and His Heavenly court has to stick to a specific time zone, it's Shabbos in one place and Friday in others. There are also two poles with no time at all (or all hours simultaneously).
There's no absolute season; when it's Pesach time in Jerusalem, it's autumn in Australia.
There are places where there is no day/night (poles) or season (equator).
Sun and other planets are not orbiting the Earth (does not really matter Halachicly), but contradicts Rambam's Yesodey Hatorah.
G-d could easily create flat and simple Earth together with the firmament, just as our Sages saw it, but He didn't. I don't see a way that the Mitzvahs observance depends on that fact.
So why G-d created the Earth spherical? What are the Halachic or other Tora-relevant issues that favor the spherical Earth?