Now, third party software, is always going to be all over the place. Stuff that was largely built on Win32 components works fine, but "modern" stylized applications rarely have strong support.
There is one major improvement you can do on Mac, at least for menus:
Qutebrowser was my favorite browser for keyboard navigation but firefox, chrome, etc. have extensions for this as well.
Look Ma, No mouse !
Well Tim, I suppose the blind do outnumber the handless.
Seeing as both can be accommodated, I would argue it's an objective limitation of macOS.
I really feel like this used to be the default. That's how I always did it in macOS going back to the early 2000's.
Only in the last two versions or so did I notice it was no longer the default. I'm glad to see here that I can now re-enable it.
Edit: I see that I do have it enabled. But for some reason there are a lot of programs where it doesn't seem to work anymore, no matter what the settings. Off the top of my head: Half the Adobe programs I use for work.
The problem is that they are less discoverable and you need to make and effort to get used to using them instead of point and click.
Economics be damned, if you're going to make a native app, use the OS provided toolkits.
Unfortunately in Excel many operations can be done only with the function keys (e.g. F2, Shift-F8). I'd argue that leaving the center of the keyboard to press the function keys is not easier or quicker than reaching for the mouse.