Do you remember 2016? Most pollsters picked Hillary to win. It was not “super accurate”. Most people were shocked by the outcome.
And no, Trump isn’t “less unpopular” than Biden. That’s the point of the article. Based on the current polls, Trump should not be struggling at all against a centrist candidate that no one knows (Nikki Haley). That’s like a pro team having trouble beating a college team. It’s not good and shows large problems.
Biden only has pressure from the left, and there isn’t even a candidate that can stand against him. The “no one” votes, are mainly people saying they want a generic progressive who doesn’t exist right now. In the general election, it’s much harder to overcome centrists who dislike you than right or left wing voters.