Oh okay well if that's how it is here, then I guess it's fine for PvP.
But what about all this easy access to 4th and 5th level spells diminishing the value of caster classes who are supposed to be the providers of those spells?
The presence of potions does not diminish in anyway the potency and value of the caster classes. They are quite useful, yes, but as was often stated, they quickly end up being of lower duration and effectiveness, as well as being easier to dispel than spells cast by actual mid to high level casters. Last I checked, parties still vastly prefer the presence of buffers in their midst over potions. Clearly the current diversity of potion is no competition to spellcasters.
While I like the idea of increasing potions weight, it would ultimately just be a change that brings disgruntlement for no appreciable gain whatsoever to gameplay. It would also be quite illogical considering that, in D&D 3.5, a potion is 1 once of a liquid held in a small glass or ceramic vial. Vials weight 1/10 lb and 1 once of liquid, using water as your benchmark, would be 0.063 pound. Consider too that these are things you are supposed to be able to drink within a 6 second round. Your 1 pound potion would be more than 1.8 cups in volume. Not very practical to quaff that in a hurry while in battle. So at 0.1 lb per vial, our potions are very nearly at the weight they are supposed to be according to the rules.
To put a duration on potions is not feasible for various mechanical reasons. Already, the fact that they are stackable items causes problems because once 2 potions are stacked the game essentially consider them as a single item with 2 charges. It cannot distinguished between the two potions to verify when one is supposed to expire vs the other. I dare not even contemplate the resources drain should the system have to track the expiry of all potions in game. To put it simply, it would make the game unplayable.