Very true, and this is in large part a function of the voting system in the US. Suppose you are choosing between primary candidates A and B, who will run against C. You'd prefer A over B, but B has wider appeal in the general election.

A better system would be a voting system that doesn't split the vote, because then you could forgo the primaries altogether. Have A, B, and C all run against each other directly. This is impossible with today's first past the post system, because that would immediately hand the election to C.