I’m not even convinced that intelligence is a requirement to be the dominant species. Intelligence is so expensive that nature rarely ever selects for it.
Trilobytes did pretty damn well for a hell of a lot longer than we have so far. I think we need a stronger working definition of “dominant” in order to judge any candidates.
On top of that, they might not even survive the CO2 and consequent ocean acidification. If humans were to get eradicated by some super plague, then octopi might still stand a chance. However, the points you mentioned mean that they are playing this game in hard mode when it comes to winning by intelligence.
I worked as an intern at a lab studying octopus vulgaris.
They are extremely sensitive to all sorts of things in the water. Keeping them well is very difficult. Although I would imagine if there are big but gradual changes in water environment, they would have a chance of adapting faster due to short life cycles and the fact that mating creates hundreds of thousands of eggs.
If we assume that they somehow survive all the way to the very moment when humans get a permanent ban to the Earth Server, then the changes should be gradual enough after that. The bad news is, humans love to play this game by recklessly exploiting every bug and glitch, so rapid changes (in evolutionary scale) are the norm.