I think the different results had more to do with the respective incumbents than the challenger(s). Cantor is singularly repulsive. Yes, Flimsey Tinkerbelle is too, but obviously not to a lot (>177,000) of South Carolinians.
Cochran is another example where the incumbent is so bad, they'll lose. But, how do we repeat Brat's success against an incumbent who doesn't beat themselves?
So why didn't Levin, Ingraham, Palin, others ... also send some love toward Lee Bright?
Nowadays, a political campaign is a long hard slog. You can't underestimate the necessary GOTV activities and having a huge network of supporters "canvassing extensively". A House seat has such a smaller area to canvass than a statewide Senate race.
Nevertheless, the Cantor defeat is a victory because other would be Rinos are in the position of the Soviets about Star Wars, they could not be sure that it would not work and Rino Republicans cannot be sure they will not be dealt out of the game like Cantor.
The point is to build momentum toward seeing the light.
And Graham isn’t repulsive?
By being better, MUCH BETTER than the opponent. The ones who didn't win when they had the backing to get the spotlight made serious mistakes and/or seemed as the campaign got rough to be less than sincere about their conservative credentials.
Look at McDaniels and Brat. They developed stronger, more focused conservative voices when they were unfairly smeared by the RINO ptb onslaught.
PS to the establishment: stopping the invasion of the US and sending home invaders is not negotiable.
When there are a half-dozen good candidates it is a lot harder for voters to get behind one of the challengers.