Earlier quoted context omitted.
Miners technically do have seigniorage authority since they can collectively decide to change the underlying cryptocurrency. Miner's de facto control of the network is a huge problem. It's why Bitcoin will never solve its energy use issue, and why Ethereum set up a "delayed difficulty bomb" to force miners to accept changes to the network.
> Miners technically do have seigniorage authority since they can collectively decide to change the underlying cryptocurrency. The failure of the Bitcoin2x proposal and adoption of Segwit in 2017 demonstrated that miners do not have as much control as they might like to think. If node operators don't accept their blocks, they lose money.
I think the exchanges have the most power, given the current state of the network where very, very few businesses will directly exchange goods and services for coins and most use of Bitcoin is done by converting to fiat through an exchange.
Looking back to 2017, there was the Bitcoin Cash fork. As I recall, Coinbase handled this in a fairly neutral way: if you held 1.0 BTC on the exchange, after the fork you held 1.0 BTC and 1.0 BCH, and trading was supported for both, so the market found a price for each. The only bias here is letting Bitcoin Core keep the "BTC" ticker symbol.
Suppose the top 3 exchanges had done the same thing, but treated Bitcoin Cash as the "real" one that trades under the BTC symbol (and is referred to on the exchange as just "Bitcoin"), and Bitcoin Core as the "fork" with a new symbol like BCC. Maybe even call it something lame like "Bitcoin Classic". Would that have affected which one won? Maybe a bit... but enough to make a difference, I'm not sure.
What if they really wanted Bitcoin Cash to win, and went a step further? What if they gave Bitcoin Cash the BTC ticker and didn't implement trading pairs for "Bitcoin Classic"? They'd still let you withdraw your forked "Bitcoin Classic" to your self-custody wallet, and you could send it from there to some other small-time exchange to try to dump it... but you couldn't trade it on Coinbase, Kraken, or Binance. What would have happened then?
There's no way of knowing, but if you asked me to guess, I'd say that what we call Bitcoin Cash today would've won. Bear in mind, for those who have strong opinions about BCH vs BTC... I have no opinion about which one is better or which one should be the "real bitcoin". I'm just speculating that, if they had wanted to, two or three big exchanges could have swayed that decision the other way.