I find it interesting that 3 of the 5 people (4 of 6, if you include the implied Senator of MS) that you use as examples of bad US Senators are Republicans. Yet, you think that it is a good long-term strategy to hold on to the one who is their leader in the Senate, their most ardent advocate, and the one who ensures that any intra-party opposition gets crushed. Curious long-term strategy, indeed.
But on a more general point, you are describing the symptoms of a neutered opposition party, not the causes. These Senators are so difficult to remove because we are in a situation where the nominal home to conservatism is actually conservatism’s most potent enemy. There is no way McConnell’s successor will be anything other than an opponent of conservatism, irrespective of rhetoric and token votes. And were a conservative to find their way to get past the hurdle of nomination, they would quickly find that they face two opponents in the general: the Democrats, obviously, and, sticking a knife in their back, McConnell’s allies.
If we have gotten to the point where we don’t do the right thing because people like Grimes intimidate us, then strategy probably makes little difference, since we have lost already.
But McConnell? Bevin was a lousy candidate, face it. He didn't have a voting track record. He had earlier signed on to something supporting Obamacare. He talked the talk, but was probably a Chamber of Commerce plant. And the appearance at a cock-fighting rally? Really? Since conservatives lost because the candidate was too imperfect, McConnell should be supported. Same thing with Roberts. Wolfe has no voting record, he was unwise enough to put patient xrays online...he lost it on his own, so Roberts should get conservative support.
The ones I see that should not get conservative support are Cochran and (in the future) Murkowski. Flake, McCain, and Ayotte (disgusting campaign liars and backstabbers). But McConnell? No, let him have those six years.