The issue is that given Biden's approval rating it's almost certain that both Trump and DeSantis would win over enough of those undecideds to at least eke out a plurality, if not a majority. I would say that to argue otherwise would be to assert an overly inflexible partisan diagnosis on the Wisconsin electorate.
Biden's current approval ratings may indicate a vulnerability, BUT people need to consider: Numbers of incumbents tend to bounce back once they actually start running for reelection. So all the talk about "he'd lose the election if it were held today" is pretty much pointless. Also don't forget that Trump's popularity hasn't soared all of a sudden and it certainly won't improve once (if) he's back on the campaign trail and people beyond political nerds start paying attention to elections again. Given that incumbency has proven to be a major factor, I tend to agree Biden would be favored, though a victory in the EC is not guaranteed by any means.
