I don't see the problem. You have high standards. It would be crazy to compare yourself to an average person in each of these situations. Do you really want to feel good about lifting more weight than the average sedentary person as a gym-goer? In martial arts specifically I think you should always be comparing yourself to the person directly above you. It's competitive and its self improvement. Slightly better is what you should be next week. A lot better is what you should be next year. The "impostor syndrome" (yes, those are scare quotes) seems like a seperate issue to me. Comparing yourself to those around you might make you feel insecure and untalented if you have a bias towards overrating others or if you are less talented but that only makes your achievements more impressive.

The scare quotes are because it seems to be assumed that anyone who has an accomplishment deserves it. Some people must luck out. If we're not going to just reject the notion of deserving entirely there must be some people who don't deserve their accomplishments and as a result feel like they don't deserve their accomplishments. Additionally, feeling like you don't deserve your accomplishment, even if most people feel like they do, doesn't mean you're pathological. People have different standards for considering themselves deserving. Some are way off one end of the bell curve but that doesn't mean there's anything wrong. When you consider yourself competent or deserving is a personal judgement. There's nothing inconsistent in an above average or even elite person thinking they are incompetent.