Although not exactly ultra-wide, on my 27" screen, the font-size with maximised window (2500px horizontally) would compute to ~22px for the submitted website. While that’s noticeable bigger compared to a narrow view port, I’m not sure that would qualify as “very large”. To me, it looks alright.

The main container’s width on their website also doesn’t scale infinitely, so on a very wide screen you’d have a lot of blank space on both sides.

That being said, it might still be reasonable to set a break point (or use CSS clamps) and prevent further font-size growth beyond a certain point.

Yes how is the viewport size really relevant? A sensible site would have a max column width for any paragraph. So if I have a 4000px wide viewport and view a 500px wide column of text, it has to be the same size as the 500px column of text also if the browser window is just 1000px?