In a medieval-esque fantasy world pre-mass-production there's no real reason to assume that potions made by two different people would be anything alike and prior experience of other healing potions may not help you recognise the kind found in the dungeon.
While that might be true, it begs the question: "Why don't all the potions cause different effects?" Not that this isn't answerable, it's just that it's equally ridiculous to claim I can identify all health potions as such simply by drinking one. They could all be completely randomly flavoured, scented, artificially coloured and etc. If there is a commonality among such items and this dungeon wasn't just created yesterday (or a few milliseconds ago) according to some narrative, then it stands to reason the identification of items in this particular dungeon -- being exceedingly valuable information -- might exist outside the dungeon prior to ones entering it. For instance, after having discovered the blue pills cause erections I could thereafter describe such pills to others; Indeed, there are many individuals who know what color Viagra pills are, and even though I've never seen one in my life, I know they're typically blue. That's because information about the pills has escaped the metaphorical dungeon, as would any such information about legendary substances.
Of course, in reality, the dungeon "magically" changes its items identification for each adventurer.
I put it to you that at character creation it's not too terrible an idea to allow some level of familiarity with worldly knowledge to assist one in identification of items.
The potion is blue, like the one your mentor gave after training, but it also looks like the one grandma used to kill weeds.As for whether this makes things "tedious", it gives a purely optional layer to the identification game. If one is so inclined they can draw out a logic graph of properties to more quickly identify items. Or, they can stick to the "classic" identification processes. I put it to you that players do, in fact, play differently. Just because an avenue is available doesn't mean one will take it "Every time". I mean, you can run any Roguelike in a VM and save scum as often as you like... but just because you can drink the potion, die, reload, then know what that potion is, doesn't mean the player will actually take that avenue.
I'm not saying it's the best mechanic, it's just one that is an alternative to the 1st post's "process of elimination" via vastly reducing types available. It performs the same function (aiding process of elimination) without reducing the types.
On the topic of realism, though; it has always struck me as very strange that some anonymous wizard goes to the trouble of brewing up all these potions and lugging them into a dangerous underground dungeon to leave them scattered randomly around the place for wandering adventurers to find and yet never bothers to actually label any of them. That's a pretty weird hobby.
Equally as strange as stuffing gold up monsters' bums.