Hard agree.Well-meaning, but not distinct or opinionated enough to offer a proper alternative for South Africa. That's both in the sense of a progressive and democratic alternative, but also as an electoral alternative.
The issue as I see it was that the internal opposition to the NP had a gaping hole in it for some years until people like Schwarz and Suzman really showed up. The United Party after 1948 was adrift, I'd argue. It took the rise of the Progressive/Reform Parties to see the rise of proper white dissidence within the old system.
As opposed to dissidence outside of it, of course.
So returning to Southern Rhodesia, the question I think, as well as electoral numbers, is would SR bring significant talent to the SAn white parliament? And would it make a difference?
Take Higgins for example. In 1930s SA he'd seem liberal, as not NP, but he's the originator of the white man and the black men must be partners, but like a horse and rider