I vehemently disagree that vertical space used is negligible. Due to standard aspect ratios, the vertical space of the display is at a premium. 1920*1080 means you have 840 less vertical pixels than horizontal - it makes a lot of sense to me to try to reclaim some of that space for actual content instead of widgets.
I would have used Full Screen Option if I could have Tab Bar showing instead of Address bar + Tab Bar. And Safari for some reason has strange GPU / CPU usage problem with full screen usage which hasn't been addressed for years.
May be instead of software design, hardware should have adopted to it. Microsoft Surface Laptop has a 3:2 Aspect Ratio. On the same MacBook Pro 13.3", that would have been an additional 120 pixel.
Another point worth mentioning, the Big Sur redesign actually have the Safari ( and macOS )Toolbar "thicker" as in taking more vertical space.
[1] I tend to hide the Dock Bar, without the Dock it is only 340 of vertical space.