Yes, you could say that ultimately the miners rule which blockchain grows, but have strong reasons to defer to the judgement core developers.
Even though the pool operators have large discretion, the computational power that makes up their pools can be moved elsewhere... a little like a transferable proxy. Most smaller miners probably trust the pools who they've grown confident in... but a large enough controversy or campaign could conceivably shift the mining-power away from pool operators who make unpopular decisions.
Yes. A large enough controversy could also threaten to devalue Bitcoin drastically. No one wants to store assets in a currency which could potentially lose the faith of all of its merchants, vendors when it forks and no one can agree on which fork is the 'correct' one. It's in everyone's best interest to do whatever it takes to get back to a single long blockchain.
Even though the pool operators have large discretion, the computational power that makes up their pools can be moved elsewhere... a little like a transferable proxy. Most smaller miners probably trust the pools who they've grown confident in... but a large enough controversy or campaign could conceivably shift the mining-power away from pool operators who make unpopular decisions.