Honestly, that's not the main selling point of vertical tabs for me. Horizontal tabs don't scale for more than a dozen or so, but vertical tabs do. The "wasted" horizontal space is useless for reading most page, but displays enough data for practical navigation, and the vertical organization allows more-developed vertical scrolling technologies to be used with the tab list (e.g. scroll wheels).
Firefox also lets you scroll the tabs horizontally. Which I prefer to Brave's approach of simply not displaying the last tabs in the bar if it's too many, which means newly opened tabs simply never show up while the others are shrunk so far they become difficult to hit with the cursor.
In the default setting, there is OS title bar, then a address+icon bar, then the tab bar.
After installing sidebar tabs, you can remove the tab bar with some css, which saves about 5% of the vertical screen space.
That's on the right track, but going too far. 16:10 or 3:2 is much more reasonable.
The idea of using 16:9 screens for work needs to die in a fire.
That said, working on a web project right now, we _are_ ensuring it looks good when maximised on ultra wide monitors, because we figure people might actually do that. But I'm with you there, for most web content it's ridiculous.
Sat next to it is a 32" 2560x1440 unit (they have near identical pixel pitch, so I don't have to worry about oddities like differential scaling between screens) that most of the time is split into two halves or ⅔+⅓ (under windows, the FancyZones util in PowerToys is handy for this).
I liked the arrangement so much at home that I've replicated it at my own expense in the office.
And since horizontal space is cheap in most websites, the latter part is less of an issue (though you still don't need it to be massive)
I can use 2 windows side by side and the pane just eats horizontal padding on most sites because narrow columns are prettier and easier to read.