If miners had to 'find something else profitable to mine', they'd just start mining
double spends depositing BTC to the exchanges that are trying to fuck them up.
They won't, because in this case miners will get fired either through PoW change or by users switching to other cryptos or leaving cryptos altogether. Miners have strong economic incentive to obey and they will, provided that economic majority is indeed a super-majority.
So now we're going to change the block structure, the network protocol, the consensus mechanism, miners' role in the process, AND the proof of work? And you still think this unrecognizable Frankenmonster will be "the real bitcoin"? Dream on.
Every time reality strikes, there is another proposal to change things. Core can write all the code they want, it still won't change the facts on the ground:
People aren't drinking the Koolaid.