We know if a majority (in terms of hash power) of nodes form a coalition, they can basically reap all the rewards by refusing to add blocks mined outside of the coalition to chain. However, this also severely damages security of Bitcoin as the same coalition can also mount double-spend attacks. It is very likely that this will drop the value of currency and hence, might be unprofitable for miners.
However, I wonder what happens if the majority just decides to agree on a lower PoW difficulty and hence, shorter block intervals. There seems to be some research that suggests Bitcoin might still be secure with shorter block intervals. See the quote from
https://www.coindesk.com/lower-bitcoin-block-time-scale/:
”According to my research the one-minute block interval seems like the most plausible. I don’t mean that it provides sufficient security, but that it would provide the same security as bitcoin has today.”
So my question is basically, is this behavior somewhat possible to observe in practice? Because if they do so, they will mine blocks more often and the blocks mined by others who follow the real difficulty will be valid too.