You're assuming studies conducted today with minimal or no replication of results are evidence of health benefits. If 5000 of scientifically less-than-perfect evidence is not worth anything, then this study is also worth nothing.
As karatinversion already pointed out, some traditional health practices have been shown to be ineffective, or even actively harmful.
There is no substitute for the scientific method.
I'm not citing it as a substitute, rather I'm saying that it isn't something you can entirely discount either. And we know for a fact that a lot of published "scientific" studies turn out to be not reproducible too, but people will continue to believe them for a long time regardless.
Nothing to assume.
Yoga and Ayurveda have proven benefits.
What method was used to prove their benefits if it wasn’t the scientific method?