So reparations or bust? Completely disregard any other (actually achievable) benefit while chasing that golden goose? I understand the frustration, but unfortunately you have to take things one step at a time in modern day politics.

1. The current system allows for less than a 50% majority to decide the president (as what happened in 2016). The current system is worse than your concerns about a simple majority victor.
2. The three biggest states do account for a lot of votes (more than a quarter of the votes cast in 2020 came from CA, TX, or FL). However, your point goes against reality - TX and FL are right-leaning purple states whereas CA is a strongly blue state. They don't cancel each other out, but they alone definitely WOULD NOT decide the election nor "dictate the other 47".
3. "neglect 49% of the active voters and groom the 51%" - You make things sound so static. About 36% of voters are moderate voters and will shift. You can't just assume that your 51% base will stay same and can be groomed. And that's not even considering that people are dying and becoming 18+ years old everyday. Politicians in a simple majority election would have to appease the general public. They no longer could simply focus on making the swing states alone happy (though, on the flip side, I'm sure they would emphasize visiting larger population states).