I think they’re both right. They’re just coming from two different perspectives. The Schaller perspective is about retaking a majority. What kinds of moves by incumbent Republicans make it most likely that incumbent Democrats will lose. The Bartlett perspective is about influencing policy. By taking themselves out of the game, Republican members of congress are whiffing on a chance to influence what happens.
Traditionally in countries other than the United States, members of opposition parties operate according to the Schaller perspective, where in the USA members of the opposition have traditionally taken the Bartlett perspective. That’s because in a parliamentary system, as an individual parliamentarian there’s really only one path to influencing policy. You need to impress party leaders and be put on the front bench, and your party needs to win the election. Then you get to play a role in formulating policy. But the American system is different and affords legislators much more opportunity to change policy as individuals. Someone like George Voinovich or Judd Gregg who’s retiring and has no chance of ever leading his party still has a chance to play an important role in shaping health care or climate policy. And the same holds for people like Susan Collins and Olympia Snowe who are too ideologically unreliable to ever become party leaders. Those folks have, it seems, a strong incentive to care more about their personal ability to impact the course of policy right now than about their hypothetical ability to help more Republicans get elected in the future.
Traditionally, this is the way incumbent senators have thought. They have plenty of influence right now but only if they bargain. So it makes more sense to bargain than to worry about other people’s possible future election. But congressional Republicans pioneered a different, more parliamentary approach in 1993-94 and are running the same play again. It’s a bit of a mystery, though, how they’ve managed to persuade members of the caucus, as individuals, to follow this approach.