and in sports like boxing there are different classes because of the differences in bodies

That doesn't necessarily make all body types equal, either. I recently started taekwondo, and based on what my instructors have said, I don't have a great body for that either. The weight class structure, and the fact that taller fighters have a major advantage because of leg reach, means that tall, thin girls have a big advance, and I'm neither–my natural body type tends towards chubby/muscular depending on how hard I exercise. Most competitive taekwondo fighters in my weight class would be significantly taller. (In terms of cardio, I'm in better shape than most people at my current level, because I do a lot of exercise outside of class, and I was already quite strong before I started...but I seem to be genetically set to have slow twitch muscles instead of fast twitch muscles, i.e. good endurance and comparatively little explosive power. And I have slow reaction times.)

Then again, other weight-class sports, like boxing, might rely less on the leg length and more just on strength, fitness, and technique. In which case I might be better off.