I think you're right about Hillary's likability which partly explains why her policies seem to be an awkward attempt to be right, smart and popular all at the same time.
I think you underestimate her as a candidate, though. Depending on who runs against her, she may stand or fall based on her likability, but that assumes someone gets a fair chance to run against her. Politics isn't an equal access contest, and you can be damn sure her connections and decades spent raising money for the DNC have bought her the kinds of favors and brass-knuckled leverage that might dissuade potential challengers from making a run at her.
I think she got a little blindsided by Obama in 2008 but also was willing to cede to him for both semi-principled reasons involving party loyalty but also for strategic reasons knowing she could resurrect her campaign easily in the next go-round.
This is her last shot now, and I think she's willing -- and able -- to call in all her markers, twist every arm and squeeze every dollar she can to get into office. Lousy personality or not, nobody else in the Democratic party has the juice to challenge her, no matter how likable they may be.
Bernie Sanders is a side show, hitting all the progressive talking points but can never attract the donor dollars for that reason. It would be hilariously fun if he would take it just a little crazier and at least feint a touch of right-wing populism on guns or immigration (the latter I think he did recently with regard to immigration and wages). I think there's an awful lot of tea partiers who hate wall street but love their guns more who might find a little honest Yankee common sense appealing.
Trump is just a clown indulging his ego. He probably believes his own bullshit, too, but he's like a sports-loving millionaire who buys a pro team to indulge his ego. Trump is just spending money to promote Trump. I also think he's potentially dangerous -- you don't do what Trump did in NY business and real estate (with Trump's personality to boot) without some brains and a lot of balls. Trump is a survivor in a city of pretty heavy predators, from Wall St. to Gracie Mansion to the unions and the garbage and building trades. He's got a zillion dollars with no strings attached and if he's not afraid of the city, the Gambinos or pretty much anyone else.