LOL funny video.
Seriously, though, drinking a potion during combat should be an ordeal:
1. Get the potion out of a pouch, backpack, untie it from your belt, pull it from a pocket, etc. I doubt PCs are just carrying them in their hands. If the potion is in your backpack or pouch, you technically have to access that item first, which also takes more time than pulling it from a pocket (depending on where the pocket is, of course).
2. Untie or un-stopper the potion. Remember, these containers hold magical liquid, they
should be well secured/closed to prevent slippage or evaporation. You don't want your potion to spill when you do a tumble or something while dodging an attack.
3. Drink the potion, which itself takes time.
4. If you have weapon
and shield (or holding things in both hands, such as a weapon and lantern, etc.), you will likely also have to drop or sheath your weapon (or other item)
before you can get the potion out.
5. Oh, and doing all of this while possibly attempting to defend yourself by dodging, parrying, using a shield, or whatever.
Sometimes people compare the time to drinking a shot or jugging a soda/beer. Well, the problem with that is a shot glass is open-mouthed so there is plenty of room for air to replace the liquid. As the video showed, in a "close-mouthed" container, that isn't the case and the air has to go in to replace the liquid--so it takes a bit longer.
When you consider all these factors, a DM is generous simply by allowing the "get the potion out" free object interaction and then use an object action to drink the potion. Depending on where the potion is stored, it could require at least another full round just to get access to the potion and then another round to open and drink it, especially if you have something already held in both hands (common IME for pretty much most PCs except maybe wizards and sorcerer casters).