Everything related to consideration of cannabis 'strains' is relative, often subjective, made worse by, as can be seen in discussions, many trying to consider more than a single differentiating aspect. Cannabis species, sub-species, strains, etc. can be defined many ways: genetic marker/sequence similarities and differences; phenotypes/appearances, such as tall vs. short, wide vs. thin leaves; relative amounts of different substances, particularly cannabinoids and terpenes; presumed regional or other source of the 'strain, such as landraces; belonging to a 'family' (or whatever can call it), such as being in haze, cheese or blue family; etc. This is made even worse by many or even most trying to consider multiple aspects, some even taking a holistic view taking/weighing all these aspects into account.
We need to realize the terminology everyone uses is funky - even scientists don't agree. As an analogy, just think how people similarly classify people, including their 'race,' using terms such as 'Caucasian' or something perhaps based on genetics; 'Oriental' based on region; white/black/mixed based on 'color;' etc. Usable terminology (can't conveniently use gene sequences) is simply non-science based, and if it is science-based, often has little relevance/correlation with other ways of looking at 'strains.' There should be no expectations of consistency or even usable definitions with most 'strain'-related terminology. Usable terms, such as sativa, indica and ruderalis, are all useful descriptors, adjectives, with overall general common understanding of their being associated with a loose collection of variably-defined traits/characteristics. And everything is further complicated by most every 'strain' having been bred, hybridized, particularly since the 1960s/70s, to varying extents.
So, addressing this thread's topic/question: Yes, in many respects 'strain' terminology as commonly used involves a lot of "BS" in the sense it's largely subjective, depends on the definition/view/biases being applied. But the terminology is useful, since there is very often common understanding in context. For example, most everyone probably thinks of similar traits, appearance, etc. when we use terms like sativa or indica here on AFN.