The facts here are simple. BTC price is dependant on USD and it can be seen by merchants not willing to accept BTC without BitPay converting them right to USD.
Now, go, run boy. Buy yourself a brain and try to debate that.
How does "being able to change BTC for X" --> "BTC is dependent on X"
In your "logic" couldn't you say that the BTC price is dependent on JPY too?
Of course merchants (and especially those with low margins) will want to have the smallest exchange risk possible and for now exchange BTC for the lower volatility currencies (ie traditional fiat).
But more importantly, how do you think BTC gets its price?
Actually yes, because JPY in turn is highly dependent on USD. Most of the dominant world currencies are strongly tied together and if one starts to fall, then it will start to take down the entire network.
When a currency has high risks of volatility, then it's a low quality currency. Merchants are not accepting BTC because it is a low quality currency. Just like it was hard to do business with Z$, that was also a low quality currency, so the merchants preferred to deal with the foreign USD because it was of higher quality.
BTC gets it's price because it is tradeble to USD and to the other fiat currencies that are also dependant on USD. Go pick up a book and read on what does it mean that USD is the most dominant world reserve currency and what effect does it give to other fiat currencies.
As long as there isn't a supplier of major resources, that is ready to accept BTC as it is, then BTC is just a gimmick that is unable to give itself value without fiat.