Not necessarily. You underestimate the degree of dislike for Hillary combined with the anti- dynasty vote. These democrats could crossover and vote for Kasich whereas they would either just stay home, or grin and bear it and pull the lever for Hillary, if their only choice was Hillary or Trump.
How does Hillary v. Kasich do in the national polling at this point? I haven't seen any polls pairing these two in a National election, but my guess is that Kasich should beat her handily because of cross-over votes! I think the Republicans better start rethinking their strategy if they want to regain the white House.
And for that matter, the Democrats should start rethinking their strategy as well. They'd do better with Bernie in my opinion. And again because of crossover vote. But this time it would be the anti-establishment crossover vote. I suppose that means a Bernie v. Kasich vote would be very close. I wonder what the polls say about that match-up.