Since Quark automatically disables a lot of its features if another mod that does the same thing is installed, it should also disable the “no potion shift” feature if any of these mods are installed:

• Client Tweaks (1.10/1.11/1.12)
• No Potion Shift (1.9/1.10/1.11/1.12)

The effect doesn't stack if multiple mods do it so I don't see the need.

Why does Quark disable its features if mods that do the same thing are installed, then?

Other features wouldn't make sense to exist in duplicate. This one makes literally zero difference for the player.