Holding $BTC imo is a good thing in my opinion as we all know how large corporations and famous people were getting into it and buying even millions of bitcoin You can also see how Bitcoin ecosystem and price are both growing year by year because of the adoptions that it is having which means that this will turn into a much larger thing on the future.
You are also talking about shorting BTC to earn from its volatility and I think its a good one if you arent planning on holding it for a long term but if you will be trading your btc, you should do it with
BTC-USDT pair as sudden fluctuations can also occur on Ethereum will might make your trade nonsense.
"Millions of bitcoin" could be a bit wrong thinking, considering even grayscale which is famously the biggest holder of bitcoin aside from satoshi himself, only has half a million bitcoins. We literally have 21 million bitcoins available when all of it is mined, now a bit over 18 million, if someone had "millions of bitcoin" you would know about it. However rest of the logic is true, there are too many celebrities, famous business people, companies, banks and many other buyers of bitcoin in the recent 1 year.
When the fiat world fails you and me, it fails those big names as well, it became such an obvious thing to not hold fiat anymore that even if you were profiting from some stock you bought, the fiat could be devaluing even faster than that, whereas bitcoin gets more and more valuable each day, so at the end of the day we are talking about something much better in logic, hence everyone is getting involved.