As much as I like to hate on a new OS like the next person, I think it's worth pointing out we're probably not seeing the full picture here: When trying to reproduce the problem as shown in the article by resizing the Safari window currently displaying the article, the drag cursor changes shape at the visible border of the window, not the shadow and consequently, dragging works as expected. https://youtu.be/kNovjjvYP…
As for the fact that one cannot resize from inside the window, it makes absolute sense for every other corner of the window, where the user would instead be clicking an icon or some other button (try the top right corner of the finder, where the search button sits).
So, while I agree on the whole that Tahoe is a huge step backwards in terms of design, this seems like an odd gripe to point out, as it doesn’t in fact seem to be an issue at all.
Edit: clarification