The 2 cents experience of a web developer:
Even before this update, I were always testing how many websites, but more important, what kind of websites were refreshed having more tab opened. This helps me to figure out the real weight of a webpage.
Now I can definitively say that, at least for me, the page refreshing is improved. I can switch without refreshing between four websites - three blogs, including the heavy Engadget, and my personal website, that is heavy too.
And if I visit only simple or light websites like Facebook, I can even switch between five websites.
Being a web developer, I daily visit the best awarded websites and portfolios in the world, and they are very heavy websites, probably the heaviest of the entire web. They also include PNG images plus alpha channel, the heaviest images on the web.
Before the update, I could rarely visit two of those websites at the same time without refreshing while jumping from one to another.
Now I definitely can switch without refreshing even between three of these kind of websites.
So, I don't know why some users can't see even a minimal improvement, but I can see it. It's obviously not perfect, but it's definitely been improved.
And I can say WHERE it has been improved: I figured out that now long and heavy pages are rendered only in the part you are watching. So it saves in the RAM only a small part of the website, not the whole website.
This method can keep more RAM free. It's the same method implemented in Atomic Browser.
In Atomic Browser, in fact, the more tabs you have, the smaller is the part of each page that is rendered.
I hope this could help.
My really two cents.