Again, you simply don't understand how their system works. It is not universal vote where you directly elect the President. Each people are first voting in their own state, and then the big electors that they elected in their own state give votes to the President. Direct elections in the US work on the state level, not national level. So your argument about "3 millions" don't make sense, since those people don't even directly vote for or against Trump.
Any other system, once again, would break the balance between states since bigger states will get too much big electors and impose their political leaders to the vast majority of states (even if they do not represent the minority of the pop). Purely proportional will basically deny the vote to everybody living in small states since just a few big states will be enough to shift the entire election in their favor. Not acceptable in a federation.
We could definitely criticize the US system, for example because of gerrymandering, wasted votes or fewer political parties, but your objection in the perspective of US system don't make much sense.