Canada

Conservative floor crossers are a clear data point that refutes your proposition. I mean, it's pretty much literal proof to the contrary.

Similarly, the liberals right leaning bias, having gained increased support from moderate right wingers, is making more far left supporters reconsider their support of the libs -- making it fair to reason that the NDP will see a bit of a bump next time.

If memory serves, the harder-right social sorts were basically annihilated in the late 90s. In 1993, the conservatives had just 2 seats. The reform party from western Canada was originally a more socially neutral / fiscally progressive movement -- it didn't focus at all on women's rights, though it did propose some modest reforms to things like immigration and the approach to quebec. It only really became more stupid, when it morphed into the Alliance, and then absorbed the Eastern conservatives to try and gain national support -- and with those eastern cons came the social bullshit. But long and short, a fiscally conservative but socially progressive or neutral party likely still has the potential to undercut the far right conservatives.