That’s the thing - you can design everything optimally.
Now, if you insist there are players going for ONLY a single thing in a game and your game is made with only that thing in mind, then yes, it would bring more fun to these players than a game being made not only with that in mind. But these players are way less than players going for MANY things while gaming.
The biggest cost in gaming are incompetent developers creating content/rules and doing 180 degrees on it constantly.