Inexcusable not to properly make two parts.
That’s definitely not enough time to properly develop and explain.
Way I see it. They should start over, adequately this time. This movie has too many flaws. They should stick to the games and only expand on what needs to.
Yeah. It indeed did not establish some key characters or moments very well. Or they could just make Warcraft 3’s story in a trilogy (that wouldn’t have anything to do with this Warcraft movie). WC3’s story is established even in the canon lore so much better and it’s quite solid on its own: WC1 and 2 might actually need more backstory explaining. The WC1 and 2 era is such a mess anyway, that I don’t really see a good arc for a movie (trilogy) there. It’s been retconned and reretconned so many times from scratch that I don’t think that even people at Blizzard really what’s the official story nowadays. 
Warcraft 3 would also have a lot more familiar characters and events for current (World of) Warcraft players: it’s quite a niche group of players who actually know the pre-WC3 story. If that was successful, maybe then they could have made the WC1 and 2 as prequel story.
Even he cant reveal his real identity, if u replay all of medivh dialogue in wc3, his speech is really too short, undetail and not convincing enough. Suddenly call all all important ppl (king, prince, royal wiz, ect) to suddenly move all their ppl to kalimdor and there will be demon without any proof/ show of prophecy magic n stuff. Even he cant show the prophecy in magic, at least he should show of his overwhelming power b4 he left, all ppl will gift a powerful being words some weight. And ofc thrall somehow believe him since he can hear the voice of the spirit which tell him to believe the prophet. but at the end, it all just a plot for the story XD
It’s how Medivh has done it since Warcraft: Orcs & Humans.
Quoting form the manual:
"Llane reaches his Age of Ascension, and the full station of Prince of Azeroth is bestowed upon him. At this ceremony, tens of thousands of devoted subjects come to offer their wishes of support and long life. During the evening feast with family, and those close to the crown, a cold wind began to chill the air. A gentle breeze at first, it grew in intensity, until the doors to the great hall were blown off of their hinges. As the guests leaned into the wind, a figure entered, riding the winds like some great bird of prey. The torches set about the great hall ignited with blue flame and the visage of Medivh was revealed. As he set down in
front of the King’s table, the guard sprang to their feet. A mere pass of his hand kept them motionless - frozen in their places. The sorcerer, now a man, explained that his years of sleep had ended. The years of constant tending from the clerics of Northshire Abbey enabled him to gain control over his powers. When his spirit and body became attuned, he awakened himself, and set out to Stormwind Keep at once. Medivh explained that he had come to repay the court for the kindness it had shown to him while he was in their keeping, and to acknowledge the occasion of the Ascension ceremony for Prince Llane. From within his flowing cloak he produced an hourglass, crafted of deepest obsidian, with sands as white as undriven snow. The young prince looked closely, but although the sand seemed to constantly sift from top to bottom, the lower half never filled, and the top never emptied. Medivh claimed that these sands represented the people of the kingdom, and so long as the glass never emptied, the reign of King Wrynn would not fail.
Six years passed, and the land slowly grew sick. Crops began failing in the richest soils of the kingdom. Children were stricken ill and never fully recovered. Even the moods of the subjects of Azeroth seem dark. The weather would become unseasonably cold during harvest, and the summer sun scorched the earth and made working out of the shade almost unbearable. Neither cleric nor conjurer could fathom what could be the cause of this change in the lands. More and more people became disheartened, and what once would have been looked over, now caused bitter argument.
During a bleak morning, Prince Llane rushed to his father’s side, carrying the hourglass. During the night, the sands had run down from the top, and it was near emptied. King Wrynn took the glass into his hands, and a chill ran through the very core of his being. As the last sands trickled to the bottom of the glass, a great crashing sound was heard at the gates of Stormwind Keep. Suddenly, the grounds were filled with hideous creatures. Gross deformities, a cruel reflection of humanity, they swarmed over the King’s guard and tore them to shreds. King Wrynn sent Llane and Queen Varia with an escort of knights to Northshire Abbey, promising to call for them when the foul beasts had been destroyed. That day has not yet come."
First of all, Medivh was the Guardian of Tirisfal, with the Order of Tirisfal being a double-tripple secret society of Demon Hunters. The amount of people that regularly interacted with the Order, let alone Medivh himself, was negligible.
Second of all, as far as canon goes, Medivh almost exclusively hung around Stormwind growing up and after waking up from his coma. His best friends were from Stormwind, and Stormwind was closest to where he built the Dark Portal and thus initiated the First War. Chances are he and Terenas, if ever, met so rarely that the King simply forgot his face, especially considering that Medivh came back aged and thus not resembling the last possible known face that Terenas might’ve had of him.
And thirdly, which is more like 2.5thly, is the circumstance that Medivh got killed a significant time before the Second War. By the time the orcs arrived in Lordaeron and when Medivh would’ve become relevant to King Terenas, M-Boy was diddely-done for.