Trump's called a sore loser because he is a sore loser. Period. He never gave a concession speech, and never will.
Instead he's going to continue to puff air into the Big Lie of election fraud, as it is the only thing going for him at this point. Without the Lie, he's just a washed-up hack: an admitted loser, and easily swatted aside by a fresher Republican face on the upswing like Ron DeSantis.
But because Trump's Lie continues to so thoroughly warp Republican politics, it's quite possible Trump still manages to beat (or intimidate) DeSantis and any other major challenger out of running in '24, due to all the logical and rhetorical acrobatics Republicans now have to pull in the face of reality about the 2020 election in order to not wind up as Party outcasts like Liz Cheney.
As a Democrat, a third doomed Trump run sounds just great. But as an American, I hate it. Citizens should be given a choice to vote on a contest of ideas about the future, not a re-run of grievances from the past. We should be better than this.
Now, about past elections.
A small faction of Democrats did indeed have questions about the '16 election. Their views, however, were rendered irrelevant in the face of Hillary Clinton's concession, which promptly occurred the morning after Election Night. There were no legal challenges to the election from Team Clinton. There were no insurrections. She went back to Chappaqua. She was scorned by Democrats as a loser, which is the more typical and, frankly, healthy response to an election defeat. She never ran again.
Going back to 2004: some Democrats had questions about the results from just one state (Ohio). Again, irrelevant in the face of John Kerry's concession, which ended any serious challenge.
Then the 2000 election, of course: the closest one we've ever had, decided by just a few hundred votes in Florida and a 5-4 SCOTUS decision. Way closer than the 2020 election. Far more legitimate questions. But after that decision came down, Al Gore conceded and urged all his followers to accept the new President.
Turns out these democratic traditions matter. We've found out that a concession speech isn't strictly necessary to turn over power from one Administration to the next, but they're sure necessary to avoid partisan violence.
The other issues you raise are either deflection or debatable.