2. I'm assuming you're talking about Chrome's SameSite value; it's worth to note that this has been rolled back a short while ago because of compatibility issues in larger government organizations having to be accessible especially now with COVID-19. More info here: https://9to5google.com/2020/04/03/chrome-rolls-back-cookie/
2. Note what Chrome is rolling back is the SameSite default change. SameSite has existed for quite some time now, in all browsers, it's just that the default is currently 'None' in Chrome but is changing to 'Lax'. So you can still take advantage of this now, it's just Chrome is delaying changing the default so that it doesn't break sites who aren't prepared for the default change.
So my point is the tools currently available really tighten up the sandbox guarantees of the browser, and make it no more difficult than necessary to build a secure site.
Perhaps, but I feel like major recent changes are fixing most of these vulnerabilities:
1. Content Security Policy locks down most of the vulnerabilities that result from something on a page being able to contact something from a different origin. Of course, it's not set by default and these days requires a lot of trial and error to figure out the "right" way to set it, but it solves a lot of issues.
2. On the cookie front, the recent changes to the default SameSite behavior also pretty much end CSRF bugs.