I read this question posted by someone else (details below) but without any response:
One thing I've noticed about newer bikes vs bikes like this [referring to a Specialized Hardrock aluminum frame MTB] from around 20 years ago is that the rear triangle of the older bikes are typically a lot beefier. on some of the newer bikes the rear looks paper thin, particularly the seat stays. What is your opinion on that trend, are the beefier rear triangles from yesteryear better or the newer, more forgiving modern frames that look like they have a lot more flex to them?
(From a comment to videoby 'madcapper6' -- though the comment was tangential to the main subject).
Firstly, is the core observation about rear triangles getting smaller accurate? Assuming its true, what's the reason for it?
This is somewhat of an opposite observation to another question (Why are bike frames getting so much bigger) which was about the embiggening of frame & some components.