Make Ctrl+Arrow Keys the default?

I'm pretty sure both are possible in xkb. But you'll have to learn how to get a custom xkb_keymap into your DE of choice. I only learned enough to do one mapping:

xkb_keymap {
	xkb_keycodes  { include "evdev+aliases(qwerty)" };
	xkb_types     { include "complete" };
	xkb_compat    { include "complete" };
	xkb_symbols   {
		include "pc+us+inet(evdev)"
		key  {
			type= "TWO_LEVEL",
			symbols[Group1] = [  Multi_key,                Caps_Lock ],
			actions[Group1] = [ NoAction(), LockMods(modifiers=Lock) ]
		};
		key  {[ Escape ]};
	};
	xkb_geometry  { include "pc(pc105)" };
};

This remaps Capslock to Escape, Escape to Compose, and Shift+Escape to Capslock. Not what you want, but hopefully this will give you a starting point to playing/breaking xkb.

Another benefit of doing this with xkb: it's now a separate codebase from X.org, and is used in every Wayland compositor I know of.

For shells (and other programs) using GNU readline for interactions and line-edits (like bash), some of this can be achieved with an ~/.inputrc configuration file, e.g., mapping the correct key sequence for your terminal emulator to the backward-word move command. You can look up these sequences using infocmp -L1 or interactively using sed -n l.

Most other shells use their own command line handling routines and configuration though, so this won't work for e.g., zsh or fish.

If your concern is about the comfort using the Control key frequently, another option is to solve this at the keyboard hardware or firmware level.

For example, I use a Corne keyboard with a control key on a convenient thumb key. I also don’t have to hold it. I can tap it and tap the next key.

Also, by holding down another thumb key on the other hand, arrow keys are available for the home row. With this, using arrow keys and modifier keys via comfortable across all apps.

https://mark.stosberg.com/markstos-corne-3x5-1-keyboard-layout/

This all depends on what "level" you want the feature to take effect.

You might have some success, for example, by generating your own keyboard table (man keyboard to start down that particular rabbit hole) that swaps the functionality of arrow and ctrl+arrow to the point that most software will think you have pressed ctrl+arrow when pressing the arrow and vice versa.

At the other end of the scale, a window manager might be able to override one or the other, or possibly both, depending on available features.

For example, in Cinnamon (and possibly other GNOME variants) it's possible to set up triggers for most keypress combinations (occasionally single keys too), capturing and processing before being passed to any software that might be running. Triggers can call commands like xdotool or anything else really. You may need to throw a sleep 0.5 before the call to xdotool in the script / command-line to allow control to switch back to the running software. YMMV.

(If you're really clever, you could assign a keypress that shuffles some symbolic links around, modifies a configuration, or some such, effectively allowing a feature to be toggled without having to modify the keypresses. Exercise for the reader, etc.)

Now does this have anything to do with why my ZSH outputs ;5D everytime I press Ctrl+Left Arrow?