Understand, this isn't a matter of opinion. If a planet is called Earth, your opinion doesn't change that. I have evidence that this world is not called Xeen:
1. There are no mentions that the world of M&M4-5 and the world of HoMM1-3 and M&M6-8 are the same.
2. Vorn 4 in Dragon Sands (why does Xeen need another Vorn?).
3. The Guardian Melian (why does Xeen need another Guardian?).
4. Mentions of the name Enroth as the world of M&M7.
And what evidence is there to support the idea that it is Xeen, other than in a walkthrough from Igromania, where Korak is a mage, and the Ancients are from Cron?
To be honest, I've never seen it explicitly stated that the planet is called Enroth.