Potions handling is... terrible. And I hate the Q key radial menu. With passion.
But you need potions especially later on, so better get used to it.
Luckily there are addons with allow switching the selected item with additional hot-keys; you would still have to press your "key to switch to health potion slot" and then Q to activate it but it's a start... anything but radial menu, yes?
You might want to look into that if you go down the potion road.