I think it varies based on the person. I view it as a combination of all of the above. His actual policies to the extent they are formalized are by and large a quasi-populism. Populism is mainstream and can be a powerful argument for the GOP (See Mike Huckabee's presidential campaign). It also the core of the message that Bernie, AOC and others are selling on the other side.
It is all the ancillary stuff around it that makes it his own brand (e.g. blowing up alliances, isolationism, etc.). Not saying that it does not appeal to people. It clearly does. I was one of the people who thought his win in 2016 was more a vote against Hillary than a vote for him, but 2020 made clear it was not a fluke for the reasons you note above, which is why Cotton, Rubio and company are lining up to be his heir. The interesting thing will be whether they can have the same success. US history has a handful of people pushing extreme departures from the status quo that rise to prominence (e.g. Huey Long), but their movements often don't survive them, which suggests that their success is as much messenger as message.
As such, the question will be is it simply his style that appeals to voters or his policies. I think there is sufficient data to support both, but my guess is it is more the former because his policy positions are a bit incoherent and non-linear such that they are not easily distilled down to a few overarching principles that can serve as the basis for a long term realignment. To the extent they are the basis for a long term shift, I think it is going to be very interesting to see if the shifts you note above are sufficient to offset the suburban college educated voters realigning with the Dems. Not that I think it guided Donald's policies, but it may represent a path for the GOP avoiding the demographic cliff that is coming by pealing off certain groups that have historically voted Dem but voted for him.
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