That is ridiculous.
In this election cycle alone, we have seen multiple incredibly weak Republican candidates win their primary elections, on nothing else but their endorsement from Donald Trump. Herschel Walker won't even participate in a debate.
That 80% you speak of, would only vote for a Republican who had denounced Donald Trump, if it was in the general election vs a Democrat... in other words, they couldn't make it out of the primary unless they had run unopposed.
A Republican absolutely does need support from Trump voters. Ron DeSantis is a terrible example for the point you are ineptly trying to make.. He has never done anything but praise Donald Trump, and that includes supporting the belief that the 2020 Presidential Election was rigged. DeSantis has also never been critical of Trump over the January 6th riot at the Capitol. Hell, he has never gone on the record with any form of criticism against Donald Trump. He is basically a Trump minion.
You are dead wrong all over the place.