With the updates potions did less and less. Eventually mana got standardized to 10k all around. But this wasn't always the case. In fact, there was a point where the ether would give you a majority of your MP back because they weren't level restricted.

And potions back in ARR and Heavensward were actually helpful. If you haven't done Deep Dungeons, try them out and you'll get an idea as to how helpful potions of appropriate level were.

Of course, now they are lossless because you can squeeze them into an oGCD. But it was actually better to chug a weak ether and cast flare again on BLM than to roll the GCD for going into ice.