not all core dev signed that i see only one, and besides core dev have no power, beacuse the miners decide, and i'm sure anything that is going to kill their profit by changing how pow work, because then you need to buy new asic probably
will be ignored automatically and never reach the proper consensus, you must understand that without the miners approval any change will not happen and it's pointless to discuss
I agree bitcoin is always decentralized that is why every updates need a concensus and the reason why scaling problem takes a very long time before it is fixed. Just like Segwit, they need 95% to approve and be activated while the one proposed by BU needs 75%. If any of them does not reach that set numbers they will not implement any upgrade or update.