Possibly, but she should have been capable of beating him. Trouble was she got complacent thinking "I can't lose to the imbecile Trump" and her rallying became more of a 'victory parade' and her demeanour became far too cocky. By the end even I wouldn't have wanted to vote for her.
Biden IMO is worse - similar to Trump in many ways in terms of age, sex, potential skeletons in the closet (though an amateur to Trump) but without the charisma. He will also suffer from Dem's being more likely to scrutinise him whereas Trump's base would vote for him if he went round to their houses and personally killed their families and Rep's are more likely to vote Republican regardless of candidate compared to Dem's. When you add in the gerrymandering etc and electoral college set-up he's got quite a task ahead of him, even if Trump's administration manages to oversee half a million covid deaths.
I personally think the problem with Clinton is she is just massively hated in the US.
I was in the States not long after Trump won and I spoke to a lot of people about Clinton and there were many who were life long democrat voters who voted Trump because they absolutely despise her, (as you pointed out about Dems above regarding the candidate), I was honestly taken aback by some of the vitriol against her.
Unfortunately that's allowed Trump to get his feet under the table and push the Trump brand, which is what I consider it to be, it isn't a political ideology. Which now means whoever is going to beat him has to have so much more about them than Biden (who I think would probably have beat Trump in 2016 if he'd have stood but obviously understandable that he didn't).
But Trump just seems to get away with murder, as you point out over COVID. Damaging the economy will probably stand against him far more than a large number of deaths.
I'm currently reading the Fuck it list by John Niven and it's set in the future and Trump has had his two terms and Ivanka is POTUS. I could see it happening. Like I said, it's like a brand.