There is zero indication anywhere - polling, electorate sentiments, rally sizes, enthusiasm, etc - that suggests they picked a candidate too late. That's simply your opinion, and it's not correct. Trump is also no longer the anti establishment candidate. He literally just did an interview/hug fest with the richest man in the world where he praised the idea of firing workers for striking for higher pay. He's a former president, we all saw what he did as president, and the people he benefited. If he wants to pretend to be the anti-establishment candidate while running on cutting corporate taxes he can certainly do so, but it's clearly not working.
Kamala has a lot to answer for in debates and interviews. But I'm not convinced most issues are going to matter in November besides the economy and abortion though. That plus high turnout tells me she's the favorite until something changes. But when does that happen? The DNC is next week. She's gonna skate past Labor Day without having a single bad day of press. While Trump flails for attention, flubs interviews, and says crazy shyt. Once again all of this is totally fine to the 46% of voters who will support him no matter what.
Wisconsin has gotten more blue since 2020. Kamala has also done a major rally in Wisconsin, that was larger than Trump's lol. And until somebody explains how he overcomes the onslaught of early voting in that state (alongside MI and PA) I'm not concerned. He simply doesn't have the bodies.