Hmm. Could that also explain the apparent ancient statues in the Black Temple/Temple of Karabor?

I doubt that those statues are of Medivh. Several reasons why:

First of all, the massive sword. Medivh was a mage.
Secondly, we know what Medivh's "hooded figure" looked like from BM and WCIII. It looks nothing like those statues.
Finally, the way they are always presented in pairs makes them unlikely to be a representation on a single God-like figure. When a statue is erected to, say, Winston Churchill, we don't make two of them and stand them on either side of a door. We make one, and put it in a public space. Also, I think those portals are actually older than Medivh.

My guess is that the stone hooded warriors are either simply generic intimidating figures (which may later be developed retrospectively into lore), or that they are representations of some elite foe we have yet to meet.

I think Roxton is right. Blizz is a great company with some really awesome lore. But, I don't think every piece of artwork/ in-game design has some tie into the lore. The two statues are just menacing figures, like a gargoyle on the roof of an old building.