There is absolutely no reason why Trump couldn't win a fair election. He's essentially done it TWICE. But, to the extent voter fraud would prevent him from winning, it would also prevent DeSantis from winning if he's serious about making real change and bucking the establishment on illegal immigration and neocon foreign policy.
DeSantis, however, has no chance against Trump in the primaries. So, even if your points were right, they are irrelevant. Trump will be the nominee.
We'll see then, won't we? Trump's constant flailing about DeSantis on social media and again at his rally today don't exactly exude confidence and security.
Unlike Trump, I'm not afraid of a competitive primary.