Primaries are a party thing. Changing how they operate is up to the parties, not a constitutional matter. You're right that the existing primary system disenfranchises voters in much of the country. Fixing that will require putting heat on the parties at the state level. The other alternative is eliminating primaries entirely by going back to choosing the POTUS, VPOTUS, and Senators as the framers intended originally.
The USA was intended and designed to be a federation of free states that were mostly autonomous. That's not absurd; it's unarguably so. The USA has become a nation-state divided into districts with a modicum of autonomy. If that's the way one thinks it should be, fine, but the constitutional system wasn't meant for that would need to be scrapped.
I disagree entirely but, regardless, the constitution includes provisions for amending it. Eliminating the EC, if it's to be done, should be done by constitutional amendment. Eliminating the EC's relevance via subversion such as the National Popular Vote Interstate Compact shouldn't be allowed.