Are most yoga classes in the US really just stretching & balance classes, and not actually yoga, since the teachers aren't yogis? What percentage is true yoga?
Having studied Yoga history for many years, a few patterns became obvious to me. The first is that Yoga has never stayed the same, and each generation of new practitioners has changed it based on their experiences and discoveries in practice, and based on the changing needs of society.
The second pattern I saw is related to this one, and that is that the practices of Yoga became more accessible to a wider range of practitioners as time went on. So at first Yoga was an arduous affair conducted with great personal sacrifice and in quite exclusive situations of exclusion (mountain caves, deep jungles etc). The earlier practices were ascetic in nature and very rigorous, not at all appealing to everyday people (or householders as we are known) still living normal lives.
But as time went on Yogis developed less severe practices that householders could follow, and over time this trend continued. We have a tendency nowadays to retrofit what we see as Yoga now into our imagination of what it was like back then, but it really wasn't the same. People use the phrase "traditional" in Yoga pretending to be somehow more authentic than other approaches but if they are in some way traditional then that simply means their practices are stuck in an earlier era and involved.
What we have today is a lighter version of Yogic practices which, correspondingly, is accessible to a greater number of people across the globe. It's not the diehard fanatical practices of mountain Yogis in the Himalayas, but that would be useless for the modern world. And yes, the risk when you water something down to be more accessible is that eventually it is mostly water.
So it's entirely possible that many so-called Yoga practitioners aren't really doing much actually Yoga (being the process of changing the mind). Or perhaps it's more accurate to say that their practices aren't very efficient and would take a much longer time to achieve the end-goal of Yogic practice than some earlier ones. So if someone who practised more intense forms of Yoga wanted to puff up their ego and feel as if they were doing better than someone else, they'd undoubtedly be factually correct in stating so (but probably such a line of thought itself would stand in their way of any depth of progress).
I say this not as finger-pointing, but as someone who previously felt this way in thinking of such-and-such yoga as being "not Yoga" and so on. In studying how Yoga has changed and continues to change, I shifted my viewpoint to realise that even if a practice is only .001% "Real Yoga" then that's better than none. Every "stretch and balance" Yoga class can help every one of its students in some way, lessen their suffering, and every time the practitioners step tp the mat they can be offered a gateway to a deeper form of practice that they may take up.
So yes, if you take an elitist standpoint many teachers, practices and classes might be viewed as "not real Yoga". But in my experience that standpoint itself may stand in your own way, and ignores the great benefit such teachers/practices/classes can have on practitioners' lives. So I'd always encourage anyone asking this (highly relevant) question whether it may be better to deliberately choose a standpoint of celebrating the wonderful access so many of us have to some form of Yoga these days, and celebrate what people can achieve with what's available, all the while encouraging a deeper search that may take them further into practice.