You can consider for example Ethereum, which has hard forked numerous times and changed the monetary policy as well multiple times. It just feels quite centralized and controlled by Vitalik. Harder to trust that crap.
Mate that isn't how it work. If Coinbase or Fidelity don't recognise the real blockchain then they no longer have real bitcoin, they have a forked coin (because they are not on the true bitcoin chain). The Bitcoin chain is determined by consensus of the majority of miners/nodes (not bitcoin holders!) and if they break from that they now have a substantially devalued asset (look up the price of BCH and BTG these days).
You seem to be under a misapprehension that owning the most bitcoin gives an institution or individual power over the network. It does not.
Bitcoin, by definition, cannot exist on two separate chains. If an institution attempted what you are saying all they will have done is reverse alchemy: turned gold (bitcoin) into lead (an unrecognised chain with no mining occurring, no recognition by nodes etc).
Let's say you have an elevator start on floor 11, and another at floor 3. The rules are, they can never occupy the same floor. Is it possible for the first elevator to ever reach floor 2? No, they would have to pass each other.
GPT-4 may be able to come to the conclusion by accident. But not reliably.
Imagine a universe with many simultaneous Monty Hall clones playing at once in many studios, where Monty doesn't know and opens another door at random. If that door has the car behind it, Monty and contestant are both shot in the head and the studio burned down and erased from all records. This bloody culling of branches of the probabilities is the same as effected by giving Monty the knowledge and telling him to act on it.
Read the original papers on them.
http://li.mit.edu/Stuff/CNSE/Paper/Hanson90.pdf
https://www.jstor.org/stable/3216893
https://mason.gmu.edu/~rhanson/insiderbet.pdf