Agree with some of what you’re saying except I think it is entirely reasonable to say Hublot has taken design cues from AP and the success of the current Hublot product line (ie. the Big Bang) is from these design cues taken from AP. Hublot’s original launch was 8 years after AP launched the Royal Oak, and yes, Hublot’s watches looked different than how the Big Bang looks like today. Today’s Big Bang has angles on the case and lug design that are very similar to the Royal Oak, in addition to the screws on the bezel. Even Biver agrees that the Royal Oak and Big Bang look very similar. Perhaps Hublot can justify the integrity of the Big Bang’s design based on the same “porthole” inspiration as the Royal Oak, and agreed, there are other watches with similar inspiration. But when it comes to design integrity even from the same inspiration, I’d have to credit the designer who was inspired first. Genta’s Royal Oak design is first and was very unique.
If you’ve ever watched Ben Clymer’s interview of Jean-Claude Biver on Hodinkee (great interview), Biver makes considerable effort to explain why the Big Bang may look similar to the Royal Oak, and the great efforts Hublot went through to try and make sure the Big Bang did not look like the Royal Oak when it was first launched. I think over time, however, Hublot made tweaks and changes to the Big Bang, which today, looks very similar to the Royal Oak.