Do some of the Alchemists potions have even have a useful effect?
Ok, I get what you saying and I understand. You don't want to upset the balance and that makes sense.
On the other hand, are things like the mega-potion of strength or mega-potion of vitality even useful when the duration is only 15 seconds? Maybe the mega-potion of intelligence could last long enough to boost 1 big attack from a mage but does it really have a useful effect. In the case of these potions that last for only 15 seconds, is it long enough and a big enough boost to have any noticeable effect at all. I'm not so worried about the cool down so much in this case.
If a potion has negligible impact, why even bother to use it. I'm a level 50 in all crafts and gathering, I collect things like pudding flesh on dungeons runs and for other items I go hunting and I don't mind spending the time doing so I save gil and enjoy tracking things down. But if I can't prove they have anything more than at most a negligible effect, why even craft them for myself to use, let alone expect people to buy them?
An x-potion or mega-potion can restore enough hp enough to give you some time if a healer is swamped with heals. It may not always be enough, but it can help.
But some of the Alchemists potions are of very dubious utility. I feel like some things are just filler for the Alchemist crafting recipes list.