Gold is just a metal and diamond is just a stone, why not we call their value too as overpriced ? Unlike crypto currency, gold/Diamonds are being valued by every part of this world ? All these people are so childish to value just a metal or a stone ?

Your old shirt will get millions of dollars in an auction if you are a rockstar. Yes, demand determines everything. Bitcoin has demand and it has value. There is no meaning of arguing it is 1000x more valued, there are people ready to buy with 1000x more so it has those values.