It really depends on the individual. All three exercises work different parts of the chest. Some people can bench alot on the flat bench bc thats all they do for their chest workouts(typical teenager who doesnt know anything else exists besides a bench lol). As far as me and my workout partners we do all three chest exercises on a rotation. So in other words one day will be uppeer and middle chest and the next workout will be middle and lower)

Some people may be really strong when it comes to their upper chest where others may be stronger in their lower chest. Just depends on the individual really. Me personally I can bench more on inclines than flat bench and the least on decline bc for a while I was so focused on building my upper chest that it just got really strong.

Did someone tell you that you should be lifting more on decline for some reason? I know some people who cant even do declines bc their legs are so huge they cant get their feet under the roller pad used to stabilize the body in place.