The crux of the argument is showing different strains requires showing different phenotypes, and that that hasn't been supported with enough evidence. D614S is

The crux of the argument is showing different strains requires showing different phenotypes, and that that hasn't been supported with enough evidence. D614S is taken as an example, which purportedly increases transmissibility (thus would be a different strain), but most-likely doesn't. Apparently the data in support of D615S is just based on it being found in a lot of isolates-- but that would also be seen in the case of founder effect.