There are ~150MM people working in US, so let's say that only these 150MM need to perform financial transactions (get paid, pay others, etc.). How many of these 150MM will be direct participants in Bitcoin? If not all of them are miners, there will be some necessary centralization.
Why should anyone trust the 10,000+ Bitcoin miners? Do I as a regular user have more freedom when dealing with these 10,000 miners vs the 4,000+ US banks?
We very well might have Coinbase, BlockFi etc. act as crypto banks, and BTC whales as the new rich. That's reward for their work and belief. What do you think is the threat vector from BTC miners? The protocol nullifies such threats.
What would be bad is if a central authority could confiscate your work output at its leisure. That's the real battle here
However, the BTC mantra is "not your keys not your coin". So if you leave it on Coinbase, you are welcoming attack by nation states to confiscate your cryptocurrency. This isn't an imagined threat. The confiscation of gold by FDR was a very real event that forced citizens to sell gold to the Government at a fixed price (of USD that the state printed at a whim) https://en.wikipedia.org/wiki/Executive_Order_6102
If BTC miners band together to cause inflation, then people migrate to ETH or <insert other crypto>. BTC loses value, and them miners have 1. not gained value even with the extra 1M BTC per block, and 2. lost value because their mining rigs generate less value per energy unit.
Not to mention, they literally have $ millions in vested interest in the success of BTC by virtue of setup and mining costs. Such a move, even hypothetically, unless it is justified somehow, will cause loss of faith in the value of BTC and the fall in the value of BTC will make them lose value in mining as they earn these in BTC as well.
So no, BTC != USD