Seems like weak sauce.
This strategy you describe cost them the House in '18, the Senate and the White House in '20.
There is no assurances that '16 will ever be repeated so the mysterious dark money bogeyman you reference are likely to be less willing to throw good money after bad.
Tr--p's approval rating among republicans went from 94% before the election to 76% on inauguration day.
These people are scared of being primaries and the strategists see much of that as a potential sacrificed seat the Dems will grab.
Independents tend not to like extremists. That's why the socialism tag worked in some districts. Socialism sounds extremist. (Doesn't matter for thus discussion whether it really is, or not.)
Rs only represent 25% of regular voters. They lose the independents, they lose!
Most of the big money people know this. Continue to fund the crazy train helps to assume wasted money.
There's no benefit to wasting the money. So, your bogeyman theory can't support it's own weight.
These people are so addicted to the rush of power that they can't envision losing that position. Those in red districts fear primary challenges more than the GE. But, it's still fear that drives them away from principle.
In fact, whether we dispose of your dark money strawman or not, you are actually supporting the contention they are cowards.
Not sure how you don't see that.