I thought about this today as well.
For the same frame design around whatever wheel size, one of those sizes will be the sweet spot, there is no way the riding experience for someone on an XS frame & someone on an XL frame is the same.
It would make more sense to not just have wheel size dictacte but to scale things like 26″ for XS & S, 27.5 for M & 29 on the L & XL.
What that says is that the bike needs to be different in many ways for extremes of height – not that you can make ‘the same bike’ with differing wheels. It won’t be ‘the same bike’, it’ll have different pros and cons that skew the design intentions (if there really are any).
I think its one we will never know the answer too, but I am certain that even the same frame in different sizes gives a different riding experience, its just impossible to quantify.
In other words, is ride/handling very different for an XS frame with 26″ wheels than it is for an XL with 26″ wheels?
Definately, but how to measure it?