Flavour in different cuts
I don't believe they are inversely proportional.  You can a tender cut that has a lot of flavor, such as a good rib-eye steak.

For flavor, the general rule of thumb is "fat is flavor".  Were not talking about all the thick and hard gristle fat on the edges, but the marbled fat speckled in the meat.  That fat helps provide flavor and moisture as it breaks down.

For toughness, it relates to where on the animal the cut is taken from.  Meat taken from areas where there is alot of muscle activity and movement is going to be "tougher" and required the more low and slow cooking approach to break everything down.  Meat taken from the opposite side of the spectrum that gets very little physical activity is going to be softer and more tender.

At the end of the day, you have to cook the cut of meat properly.  You can make a tender cut tough and a juicy cut dry if you don't cook it right.