I am blacking out my bike anyway, I'll replace with some plastic black strip.
Thing is, if it is made out of a wrong metal, cleaning it makes no sense, as it will rust ASAP again. I don't want to maintain it, specifically, if it can be replaced with a worry-free alternative.
Yes, I probably could make a case for warranty, but it being decorative, I think it doesn't rise to the inconvenience of driving to the dealer and waiting for them to swap it out. Even then, are they swapping it out with the same strip made out of the same metal?!? For the price of the bike, they could have done the strip out of 316 or 316L. Not that much over 304. At this rate of rust, not even sure it is even 304.
Consider UK being surrounded by salt water. I bet their engineers have a good understanding of rust.
Overall, it is NOT a big deal at all. I am just taken aback that on such a $$$ bike it took so little time for something to start rusting. Yes, I am happy it is not a major component, but my cheaper bikes took like 8-12 months to develop their first rust. This is a premium bike.