If you are a Dex based fighter/ranger/monk, you would get nothing out of the elixier apart from maybe a higher carrying capacity and the bladelock can use their charisma stat right when they get their subclass, so again, why would they need a strength elixier? You don't play half of the game with the wrong stats and then change your playstyle completely.
As The Old Soul says above.
The way the game works is that the weapon attack/damage uses the highest score. A dex based fighter using finesse weapons will still *default* to the strength score if it is higher than the dex score. Same with the pact of the blade warlock. It's just the game mechanic.
So a dex based fighter using the potion doesn't actually use dex until around level 8. And then the dex is just equal to what the strength has been the whole time.
The entire point is that the potions undermine the martial builds. They're abundant. They're long lasting. They're easy to get. And they're not expensive. No one's saying every character has to use them after every long rest, but having one character use them consistently breaks the basic fundamentals of the character build.
