I tend to agree with 1 BTC = 1 BTC.
I am always surprised when I hear people say this. I don't really think they believe it themselves, or they might think that way when it benefits them. If you think 1 BTC = 1 BTC, and it will always be 1 BTC, then the same logic should be used in situations that don't benefit you.
You are changing the context and yes in the context of
exchanging bitcoin with something else it makes sense to talk about its value against that
thing whether it is fiat or an object like a USB.
But in
the purely bitcoin context, 1 BTC = 1 BTC. For example when price was $3,000 you were paying minimum of 1 s/vb and when price went up 10 times and reached $30,000 you are still paying minimum of 1 s/vb because 1 BTC = 1 BTC. And if you had 1 BTC that was worth $1 and wanted to mix it you still use 1 BTC, and if you had the same 1 BTC when it's worth $40k you still mix 1 BTC.