As for MUI, it was a fantastic system for programming user interfaces and for displaying user interfaces, and it's one of the great tragedies of computing that nothing of that calibre exists today as a cross-platform user-skinnable UI toolkit.
It was however, very slightly lacking (on the Amiga) as a system for using user interfaces because it lacked that sense of immediacy for which the Amiga's UI was previously known.
With traditional Intuition gadgets the rendering was done within a high-priority system task, so if you click on a gadget you'll get immediate visual feedback even if the application isn't ready to respond. With MUI the drawing, and thus feedback, doesn't happen until the application's paying attention. Because of that, MUI applications felt non-native. (Even Windows-like!)
That might not seem important in today's world where that level of responsiveness was burned on the altar of network backends and web presentation layers, but that sense of "having the computer's full attention" is a big part of why the Amiga still has fans today.
The solution is simple. If you don't know correct font size of every visitor, don't change the font size. Each visitor will have font set according to their preference. I will have set it to medium, my grandma to xx-large, teenager with perfect vision to small, designer with 8k monitors to 150px helvetica.
If you want to retain some control over the font size, use small, medium, large. (e.g. information dense site could use small, average website like yours could use medium, and information sparse websites like wedding announcement could use large).
I started making my own small, monochrome icons for a personal project (https://anachronomicon.coldewey.cc/), trying to make them reasonably small while also intelligible, and it's hard once you go below 24 pixels or so! I haven't stuck to any standard size either, but I might later. 32 seems luxurious to me now.
It's hard to actually tell from the images on the site (they are all really really large and you can usually only tell the quality of an icon by seeing it at the size the user would).
Any chance you could make a small addition to your site so that your set of icons is displayed at 100% size? Right now it's scaled up about 1500% of the original size.
Then, once, a designer friend was doing some UI and I suggested using icons instead of edit/view text or something like that, and he replied "I don't believe in the thaumaturgic power of icons" and that somehow changed my perspective forever.
The user won't learn a UI from icons alone, but once learned, distinct icons speed up recall massively. The problem with the modern trend of hyper-homogenised, uniform icons is that they destroy this advantage. When every icon has the exact same stroke weight, color, and geometric bounding box, they blur into a useless mush.
xOS '27 basically miseducates users into doing that by offering to give the Dock or Home Screen icons of the same color.
