I understand that claim. I will not even argue against it. But, as you pointed out - there are two options only, so they must be evaluated against each other. Ds would need to go quite a bit further in the direction of being fiscally conservative to justify overlooking their other issues (in the eyes of R voters) in order to capture significant voter counts from the R side.

"How tasty would the beer need to be to justify the burned rancid steak, to make this diner better than the other one?" -- basically