What do you mean by one BTC will remain one BTC even if the demand decreases? Are you not aware of the supply and demand rule and how it works? The price of Bitcoin or any commodity or thing increases if that commodity or thing gets a higher demand if it has a limited supply, and the same thing happens in the opposite way if the demand drops.
The interest rising or falling may don't have any effect on the network and it will obviously continue to work stably, but that does affect the market in general, in terms of monetary value. Bitcoin and any other cryptocurrency with a limited supply need higher demand to have a further increase in its price.
Bitcoin was meant to be used as an alternative to Fiat in the first place. Not as something you can hoard for profit. Theoretically, 1 BTC will always be equal to 1 BTC no matter what. The problem is that people are measuring BTC's value in Fiat terms. If they did use BTC regardless of market prices, things would be a lot different now.
I'm waiting for the day when the world ditches the "Fiat Standard" in favor of the "Bitcoin Standard". Once that happens, BTC will be used as the main unit of account (meaning everything will be valued in BTC terms, not Fiat). Why would I care about Fiat inflation, especially when it's doomed to failure? We should focus more on filling our bags with Bitcoin, as it's sound money that can't be controlled or debased by anyone. Supply is fixed to 21m units, so there's nothing to worry about. Who knows how far BTC will go in terms of mainstream adoption? Just my thoughts