Bitcoin is valuable because it is useful to people. If what you are saying is true, then it would apply to everything that has a dollar market. I'm sure you don't think gold/oil/etc have value solely because they can convert to dollars.
Pretty apagogical argument here
But it seems you draw the wrong conclusion from it
It's a good proof of concept, but for now, what bitcoin is useful for? In the real world, I mean...
I ordered food for me and 11 friends online. Payed with a super easy to use Bitcoin app. While everyone was watching the transaction went trough in less then 3 seconds and the food was delivered half an hour later.
The food delivery company using BitPay probably payed a lot less in fees compared to the traditional methods we had before Bitcoin.
Everyone is happy. Me, my friends, the delivery company and BitPay.