LOL what? That's like a skateboarder saying, "check out this omnipotent kickflip!!" I'm pretty sure the term anti-climactic isn't meant to be used like that. This mechanic was planned to be in the game at some point, but was reasonably scrapped.
What if you could empty multiple potion bottles into a cauldron, and then when you use a bottle on it, you get a potion with mixed effects (with shorter effect duration).
Because that would be horribly overpowered. There's a reason why potions don't stack, even if they are the exact same type. Potions can be extremely powerful and can really turn the tide in most situations, especially when you mix a bunch of them and are able to make yourself a speeding tank with night vision and immunity to all fire.
Having one strength potion can potentially be enough to make you all beefed up. But walking around with a Strength + Fire Resistance + Regeneration + Water Breathing + Night Vision would be enough to despawn all mobs in the game out of sheer fear. Even with the 20 seconds thing, the possibility of being overpowered is still there.