I like the idea of BTC and ETH serving similar purposes as Gold and Silver. BTC has scarcity going for it, and ETH has been deflationary for a while. Seeing BTC have a lot of transaction is interesting, but I don't see it being the norm. As more BTC are stored in ETFs, the liquid supply should get lower, and the transactions should follow.
I would agree with you, if more entities hold Bitcoin as a reserve, that will mean less of it out there. That would likely mean it could end up with transactions following, at least for BTC itself. You might get a lot of activity on things tied to it like ETFs or wrapped tokens.
As for the gold and silver, time will tell. It is possible that Bitcoin does take over for gold. In the digital age, this makes a lot more sense. There is also the generational thing to consider.