Every time anyone brings up a problem with Bitcoin someone says this. It seems like bitcoin is not designed for anything but existing.

Exactly right. All needs to do is outlast everything else. This where the store of value narrative comes from.

And when it goes down 75% in a few months it doesn't matter because if your intention was not to "store value" until the end of time you're doing it wrong. HODL!

Indeed it does, but generally in industry and technology one goes from inefficient prototype that serves as proof of concept to a more efficient one. Do other cryptocurrencies not improve on Bitcoin in some way? If so, why does it continue to have value despite its agreed-upon flaws? If not, why do they have any value?