The ISO does not change how much exposure the film gets, but it changes how much exposure the film needs.
I certainly consider ISO a factor. I like very slow film for some things, as I like long exposures, with blurred crashing waves, that kind of thing.
I'd love to see a forgiving C41 film like Portra 400, but with an ISO of 25 or something, would be really interesting to use. I could get an ND filter I guess.