That's a standard compact Mac layout, so muscle memory will work fine for Mac users. Maybe Fn is elsewhere for the PC one, but I detect a tiny bias in the website.
Whilst I always used a full keyboard with a PC, for the reasons you give, the Mac has practically all of those things mapped to cursors + meta keys so your hands don't need to move from the normal typing position. I now see the extended bit of the full keyboard as dead space that makes me reach further to get to mouse/trackpad. But as you say, everyone is different.
Right. I use a left-handed mouse due to RSI, so 100% keyboards are not a problem for me, and moving my hands around a bit rather than using chords also helps with the RSI. It also reduces the complexity of chords when using keyboard shortcuts like Ctrl+Shift+PgUp, or NumPad-specific keyboard shortcuts (like Ctrl+NumPad-“+” to auto-fit columns in grid views, or Ctrl+NumPad-“*” to expand all subfolders), which I do a lot.
Whilst I always used a full keyboard with a PC, for the reasons you give, the Mac has practically all of those things mapped to cursors + meta keys so your hands don't need to move from the normal typing position. I now see the extended bit of the full keyboard as dead space that makes me reach further to get to mouse/trackpad. But as you say, everyone is different.