Would be curious to see if our resident Chicago expert makes an appearance, but from the outside looking in, we really have this split between what Twitter/Reddit/etc. think is going to happen (ie. Vallas has a ceiling, Johnson will win the lion share of the other candidates vote) and what is more likely to happen in this case (ie. voters are complicated, some subset of Chuy/Lori actually will vote for Vallas over Johnson).
If Vallas had won between 25-30% of the vote, the split is maybe more difficult for Vallas... but at 34% in the first round, I just see a lot of people overestimating how much it's going to take for him to win.... he really doesn't have to pick off that much to get to 50%+1. And for better or worse, his base of voters actually shows up at every election.