We are in the scenario where all pools agree upon a protocol, and the full nodes want another one. Pools only care about their block being accepted by other miners
nope. because IF pools right now made blocks 465623-465723 that were, say using MD5 hashing..
by this evening.. they would find out that all the merchants wont see their rewards of 465622+
the pools would have most definetly realised that merchants wont buy their 465622 reward by at most 465623
Stick to the case where all miners agree on a set of rules, where the full nodes don't agree with, if you want to show the power of full nodes imposing their rules on miners.
so pools wont continue making md5 hashed blocks for 16 hours
because 1 pool will see a nice easy income by switching back to sha256 and win every block that is spendable to the merchants and have no competition