I understand.... I think point number two carries a lot less weight given the nature of these voters (Biden 2020 voters -> undecided), ideologically, they are not fellow travelers with Trump. Point number one is theoretically possible, but for Trump's campaign, it would be dangerous to rely on this happening as it is something that is out of his control and, by and large, would require some massive mistake / black swan event that would damage Harris.
Your second point will matter more as we get further into the election and the battle starts to be over swing and undecided voters... as far as definition is concerned, it's honestly been shocking at how ineffective they have been at trying to define Harris, and it seems like the month between the Biden dropout and Chicago is an extremely important time for which to do it. A lot of it has to do with the fact that commercials / paid media can only do so much.... they have some ads out hitting her on the subjects you would expect them to, but they only go so far when the guy at the top can't hammer a theme and rambles about other, less effective **** when rallying (ie. culture war ****)
Overall, the bigger piece that I think Crosstab Hater is getting at is understanding why pre-debate polls were showing what they were.... despite the framing of there being many Biden->Trump voters by many pundits, the polls almost always were showing Biden lagging in share among Dem voters. Which means it was all about enthusiasm, and that the voters were being lost either to the couch or to third parties. With Harris in the race, that dynamic is upended. And it's hard to see with that particular dynamic being upended how it could be attributed to an ephemeral bounce or sugar high.