Even with a few years of political experience, Stewart would be seen as too much of a polarizing 'Hollywood elite' type to do as well as Biden did. He would lose the EC but win the popular vote, similar to 2016.
Stewart has done a remarkable job appealing to and standing up for working people though. I don't think he would have the "Hollywood elite" image at all, certainly not as much as someone like say Bill Maher.
He's also highly charismatic and persuasive. Even the Newsmax comments seem to largely be reluctantly siding with him after his interview there yesterday. If he can persuade a Newsmax audience, I have a very hard time seeing him lose Pennsylvania in 2020.