As for why the RNC didn't sabotage Trump in 2016 the way the DNC sabotaged Sanders? I believe that giving Trump the nomination was their act of sabotage. They meant to throw the General Election to Clinton by tossing a dud into the ring with her, to give her what they assumed would be a layup.
Except it didn't work out that way. We did what we weren't supposed to do -- what the establishment, high on its own supply, assumed we'd never do. We voted for the orange clown instead of the Wicked Witch Of The Beltway.
2020 was the establishment, wary of that, making damned sure that even if we did it again, it wouldn't count.
Anyway, going back to your original thought: No, I won't be shocked if what ought to be a red tsunami in November "mysteriously" fails to materialize. 2020 proved that elections are nothing but theater to keep the peasantry from taking up arms and ending this clownshow with richly dressed bodies swinging from lampposts. The danger to the elites at this point is that most of us have gotten wise to that now.