My only problem with the mesomorph part is you can sum it up by saying don't worry, be happy! Which is kind of true I guess... you do gain well without gaining too much fat when you have this body type...
I actually read a book on body types which was more like Eastern mystical stuff than anything. They said that mesomorphs have so much power and energy that they can easily create an "excess" of energy/power by eating too much meat protein. It also claimed that we have poor digestion of raw vegetables.
So I tried some of the suggestions for awhile - fewer calories, less meat, more vegetables (cooked), less weights and more running, a lot more focus on flexibility, swimming, etc. and you know what, I felt better and didn't lose a whole lot of muscle mass while I was trying those suggestions. These points are probably true if your goal is to feel healthy and live long.
But if you want to run a 9.79 100 or just have rock hard muscles and stare at yourself in the mirror, I guess you have to hurt yourself by becoming too strong "for your own good."
I do think a lot can be explained by body types. Mesomorphs gain muscle easily especially on cycle, so the weak link will often be their joints. I am sure all body types have problems, but endomorphs tend to be big-boned and tough enough to take heavy weights. Heavy weights will do great things to my muscles until they start to outstrip my elbow joints' ability to keep up... and my hamstrings and hips are tight as hell all the time...