I'm gonna bite on this example since you chose such a good one: if the convention on the platform is that `Page` buttons are like scrolling – NOT like arrowing – then good applications should respect that convention.
You personally list this particular (mis)behavior as a "plus" since you like the PC convention better. But another person will think the opposite. Objectively, it's simply just inconsistent.
What we need is "good platform citizen" apps which respect the local conventions, and you as the user get to choose the platform with its set of conventions you prefer.
What we DON'T need is apps "unifying" behavior across operating systems based on their own opinion of what's better, ultimately just creating more mess.
Many of us on the Mac are there in part because the environment and conventions make more sense to us than the conventions on other platforms. X-platform apps typically ignore this.
However for keyboard shortcuts said conventions are defined for crippled keyboards without dedicated navigation keys and the extension for PgUp/Down is simply inefficient when programming.
The cursor movement conventions have existed in macos since the classic mac days, when Apple was routinely shipping keyboards with "dedicated navigation keys":
Up / Down: move cursor one line up or down
Left / Right: move cursor one character left or right
Option+
Up / Down: Move cursor up or down a whole paragraph
Left / Right: move cursor left or right a whole word
Command+
Up / Down: Move cursor to the beginning of the document
Left / Right: Move cursor to the beginning or end of the document
Page Up / Page Down: Move the scrolled display area up or down a "page" without moving the cursor
Home / End: Move the scrolled display area to the beginning or end of the document
The latter two are nice to have because it means you can scroll up through a window to view something, and start typing to have your view snap back to your cursor position.
Additionally at least as far back as the Powerbook G3 "Wallstreet" in 1998, and including the iBook lines from the same time period, to the best of my knowledge every Apple portable since (as well as any wireless/compact keyboards with Fn keys) then has supported Fn + Left/Right for Home/End respectively and Fn + Up/Down for Page Up / Page Down respectively. They were even marked as such through the early non-unibody MBPs but continue to function that way today even without the markings. While these aren't dedicated keys, they're convenient enough in combination with the other modifiers that you'd be using to move the cursor that I don't personally consider it a significant difference.
I think there's a somewhat obvious middle ground here: use the platform's default behavior, and surface an option that lets a user decide if they prefer the other version; eg: a PC user should also have the option to treat the page keys as scroll inputs rather than cursor navigation.
Answer to your Answer: Then its on the application developer to give you the option to override the platform convention, but well behaved apps should adhere to the conventions of their platform by default.
No, you don’t get to decide that. Myself and many others have decided they liked this unified behavior just fine, while still preferring to code on macOS.
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You personally list this particular (mis)behavior as a "plus" since you like the PC convention better. But another person will think the opposite. Objectively, it's simply just inconsistent.
What we need is "good platform citizen" apps which respect the local conventions, and you as the user get to choose the platform with its set of conventions you prefer.
What we DON'T need is apps "unifying" behavior across operating systems based on their own opinion of what's better, ultimately just creating more mess.