You know, the CTRL-Fn combinations are usually mapped to virtual workspaces on Linux, what is much more powerful than applications and give you the same kind of speedup.
Who organizes things around application anyway, instead of windows?
Anyway, no, it's bad to remap the Fn keys. They have been used to fast intra-application navigation since they appeared, and they are still in wide use. (Does the author not use application shortcuts?) Combining them with another key is just obvious.
> Who organizes things around application anyway, instead of windows?
macOS. There's no Alt+Tab, for example: no way to switch between two arbitrary windows on the Z-stack¹. The not-equivalent that exists is ⌘+Tab, and it switches apps; the usability of it, vs. Alt+Tab, is horrendous. (It fronts stuff you don't want, covering up stuff you do want.)
There are workspaces … but I have found them hard to get productive with: macOS will reorder keystrokes around workspace changes. That is, the keyboard input "abc ^→ (workspace change) def" is a race condition: typed quickly (within the animation delay), it becomes as if you typed "abcdef ^→".
¹no, ⌘+` does not count.