All good points, and no disagreement. It's been despairing to watch the Democrats go through the same circus all over again. But the chief reason he would win again is gerrymandered districts, voter suppression, disinformation campaigns, a compliant Senate, the Electoral College, stacked courts and other shenanigans including likely election interference. The GOP does not even hide this these days. Here's something Trump himself said about Democrat proposals for increasing voter turnout and ensuring access to voting for greater numbers of people, including vote-by-mail: “They had things — levels of voting that, if you ever agreed to it, you’d never have a Republican elected in this country again." They know that the US tends to lean slightly Democrat in the 21st century.
What gives me a little hope is the recent Wisconsin State Supreme Court election where the incumbent Republican judge was pretty soundly beaten, despite the state refusing to postpone voting during the pandemic yet not sending out mailed ballots, and forcing voters to vote in person. Those sorts of elections, however, do not necessarily translate to the general.