I think there's two factors that people often neglect when they suggest that another Republican would be doing better: 1) that these republicans would lack the ground swell support that Trump gains both from the base and those who normally don't vote, 2) the career-politician, corrupt-insider claim against Clinton falls flatter with career politicians making the claim. Kasich is more like Pence than the primaries showed. He's darn likable but he's swallowed by his religion. For instance he proposed an agency to promote "Judeo-Christian values." I imagine there's a bunch of stuff that would be unpalatable to moderate, secular Americans. All that said, I do think Kasich would be polling ahead though the electoral math would still be unfavorable. In the end I think Kasich wouldn't make the arguments against Clinton to rally the base, and gets the losing side of the Bush v. Gore election.