Obama is the only black person to have reached the summit of US politics, and is an extraordinarily talented politician. Regardless of whether you agree with him or not, he is probably the most talented politician to reach the summit since JFK. The fact it took someone as talented as Obama to get through the glass ceiling shows that, yes, things are that bad. The fact that his successor was someone as uniformly talentless as Donald J Trump, whose main electoral plan was to claim Obama couldn't possibly be American because he is black, only proves it.
What you don't see is mediocre black or Hispanic politicians reaching the summit. There have been plenty of mediocre white men reach the top though: Bushes senior and junior, Gerald Ford and Jimmy Carter, not to mention the current Chimp in Chief. And that's really where you measure equality: can mediocre people from one race rise as far as mediocre people from another.
I fear you're trying to deduce too much from limited data, and making too many assumptions.
Firstly, I doubt anyone would dispute that the situation for blacks in the USA was absolutely terrible until at least the 1960s. So any elections before then are irrelevant to the question of whether things are that bad
today. If we say, go back to 1972, there have been 14 presidential elections since then, and Obama won two of them - so a 14% success rate for (currently) 13% of the population. Doesn't seem that bad, but obviously that's not nearly enough data to go on. No presidents from non-black ethnic minorities seems a bit more damning, as well as no female presidents - but 14 elections is still not a lot of data. The other thing is, it takes time to become well known and respected enough in politics to have a good chance at running for President (usually anyway; Trump is a bit of an exception probably because he knew how to appeal to populism and was lucky enough to have a particularly unpopular mainstream opponent at a time when trust in mainstream politics was very low) . So even if, miraculously, things became completely fair and equal tomorrow, you'd probably still be looking at, maybe, 10 years, before representation caught up.
Also, I'm not sure I'd describe Obama as 'extraordinarily talented'. If anything, he struck me as being full of good ideas, but somewhat ineffective at implementing them. I suspect that may be in part because he ran for President without first taking the time to get much experience in national politics, although the obstructionism of the Republicans wouldn't have helped. At any rate, who gets elected seems to me to be much more dependant on knowing how to appeal to voters than on being talented at running a country (the current Presidents/Prime Ministers of - for example - the USA, the UK, and Brazil all amply testify to that!)
Churchill was a thoroughly unpleasant chap, even for his time. That's why he was such a good wartime leader and why, as soon as the war was over, he was voted out.
Yet 6 years later he was voted back in again during peacetime (albeit in part due to the problems with our electoral system). I think you'll find there are other reasons why the Tories lost in 1945.