I find that rather silly, personally-- but that is just me exercising some domain knowledge.
(Learned all kinds of fun stuff when I studied magical practice as an independent study of anthropology. One of the avenues I explored was creation of tinctures, potions, poultices, and the like.)
Some very effective "Speed buffing" potions can be brewed very inexpensively IRL, if you dont mind the side effects. Take for instance, a slight bit of a toxic mushroom (Amanita Muscaria), added to a tea made from Ephredra. Dark age speed in a bottle right there. Side effects include euphoria, and hallucenations. Routine use can lead to heart and liver damage.
This is exactly the kind of thing I would expect an herbalism specialist witch to know. As such, I consider the "Cure alls only" restriction absurdly out of touch with the archetype they are going for there. But hey, their game, not mine.
Maybe I should just sit down one day and crank out a couple fun lists of things that could be cooked up using just a tea kettle and some wild plants some time, and leave it as a community source book. Unless you need to use gold as a reagent, I really don't see a valid reason to require GP expense on potion creation-- aside from if you need to pay somebody to do some ingredient gathering, or to perform some of the process steps for you. It should be mostly be initial equipment costs, (you DO need some specialist equipment to brew the more interesting potions from dark age literature), and encumbrance from carrying that stuff around.
I get a little annoyed with some of these games' rules sometimes. (Yes, I understand the gold requirement is to stop you from brewing shitloads of potions and generally ruining the DM's day. Personally, I think that same effect can be obtained by forcing the PC to buy the required bottles to hold the potions in, and forcing them to have to lug equipment around. Abuse of potion would be more interesting to deal with by adding consequences to misuse, such as the side effects, and effects of heavy use, like the potion mentioned above. Not all potions can be stored in clear glass bottles, as some degrade from exposure to light, and need to be in dark brown glass- others can react with metal oxides in colored glass bottles, so that's a very reasonable requirement for some potions right there that would naturally limit abuse. Adding encumbrance for empty bottles, and having the skill tree to make glass bottles not be included in potion maker classes would also naturally limit it in a more organic and less contrived way. Basically, I really think this can be handled much better, and the game rule makers are either covering for ignorance, or are just being lazy.)