The more I get into Bitcoin and crypto, the more questions I have

I've been getting into crypto since the start of the year. Dipping my toes in, so to speak. I've got some BTC, ETH and a few altcoins (mostly top 10). When I started I thought I just didn't understand it and I needed to do more research. But the more research I do, the more questions I have.

Bitcoin maxis say Bitcoin should replace fiat and the banking system. Michael Saylor himself says Bitcoin "is money that won't fail you stored in a bank that can't rob you"

Let's pretend this scenario actually happens. If Bitcoin replaces the banks and is the new currency for the world, how would it even be practical for everyone in the world to adopt it? Bitcoin has a finite supply, so late adopters are likely to get in at a higher price meaning they'll have less Bitcoin wealth to their name. In the best-case scenario, won't this just change shift wealth to a new wealthy class who were early bitcoin adopters? (assuming people wealthy in fiat aren't holding most of the Bitcoin already)

Bitcoin is championed as decentralised, but when the top 10% of miners control 90% of mining capacity, is it really as decentralised as everyone thinks?

How could Bitcoin possibly handle the instant transaction demands of billions of users when the average transaction speed is approx 10min while only having millions of users?

If layer 2 solutions (like Lightning) are required to enable Bitcoin to scale by using off-chain transactions, doesn't that make Bitcoin less decentralised?