When there are fixed election cycles, one can hold open primaries and the power to select candidates can be taken away from party central offices. This thread is explicitly about the fact that Donald Trump is positioned to possibly seize the presidential nomination of a party with which he has never had much meaningful association. So your first paragraph seems odd to say the least.

As for the Electoral College, first, your assertion would seem to imply that the possibility of more than 50% of voters in a representative district being assumed to be represented by someone they did not vote for is somehow nonsensical, and second, the states can decide to allocate their electoral votes through whatever system they desire. On a game theoretical level, the system is driven at the first mover level by the smallest states. If Delaware guarantied a net one vote return regardless of outcome instead of a net three votes to a winner, then national candidates would completely ignore the state. As states get larger, they adopt the same strategy to maximize their impact. By iteration, the dominating strategy gets adopted by every state (minus two). the outcome is what is called a Nash Equilibrium.

As an extension of the first point, in the US, supporters of the Democratic Party are much more likely to live in ideologically homogeneous areas compared to supporters of the Republican Party, and therefore, "safe" Democratic Congressional districts tend to be much more crowded with Democrats than "safe" Republican districts absent any gerrymandering, so any localized district voting system will favor the Republican Party in the US.