If Trump won in 2020, Pence would be the frontrunner, probably wrapping up the nomination easily with Trump's endorsement.

The Democrat primary would have been contested rather than a walkover for Biden. There's no reason to believe Harris would have received more delegates than in 2020. If Harris did really well, she might get 10% of the primary delegates.

The only reason Pence became hated by the right-wing is that he didn't do what they wanted during the vote count on Jan 6. I.e., he followed what a majority of Congress said the vote count should be, instead of ad-libbing the idea of tossing electoral votes he didn't like. There's no point repeating that debate here. I still say that, if Pence did what the right-wing Trumpers wanted him to do, he would have been voted down in Congress and there might have been an emergency lawsuit filed that he would have lost.

However, after that, Pence seemed to double down instead of saying "I didn't really have the power to do what people say during the vote count." Instead, he went hardcore never-Trumper.