Well, to be frank, i didn't automatically assume Ganna was going to win but it would 've been most likely i guess. However, van Aert "only" finished about half a minute down at the WCC, the smallest margin between winner and runner up in some years. While the context is important, since van Aert came out of the TDF where he was working each and every day, while Ganna had an ideal prep towards the WCC. Then, knowing van Aert is supposed to be in top shape in 2 weeks, while Ganna is not, you know something like this could easily happen. The moment Küng beat Ganna's time, i was kind of expecting van Aert to beat both.
I also find it remarkable that everybody simply assumed Ganna turned into some unbeatable force overnight, at the exact same time as Evenepoel got injured. As if Ganna acquired superpowers the moment Evenepoel fell off a bridge somewhere. Ganna was beaten by Dennis and Evenepoel at the previous WCC, by a much larger margin by both, than he beat van Aert by. He was beaten by Evenepoel at the Euro's. He was beaten by van Emden at Chrono des Nations, and then he was beaten again by Evenepoel in San Juan. Evenepoel continued to beat Dennis in Algarve, then he crashed and Ganna became "unbeatable".
That said, i would not read too much into it. It's simply what commentators do (maybe have to do). Whenever somebody wins it's "a staggering performance" and everything is in hyperbole. Take van Aert's win for example, Sporza described it as he "blows Ganna & Küng away"... ok, he won by 6 seconds. While an amazing performance on its own against these two and on a short itt, he didn't exactly blow them away, imho. Roglic was unbeatable, set in stone, until he lost. Both the Giro, TDF and PN. Those races didn't have to be raced basically. Yet they had and he lost them all.
I think it's also important to note that such behavior by commentators tends to annoy us a lot quicker when talking about other riders, than the riders we support. Maybe i can't speak for everyone, but i'm sure more often than not, that's the case.