Did they change the AI difficulty in the last ~1.5 years?
Just started playing again for the first time in a year or two and I easily beat the hard AI twice, hardest once, all first try. I was rarely able to beat the hard AI before. And I beat the extreme AI on my 2nd try just now after a rematch (same map, civs, etc). The extreme win might be a fluke, especially since it was a rematch.
The one thing I could point to having changed is I just stopped stubborn habits and responded to change more easily - switching units when seeing what they're responding with, taking my focus out of a hot area and tending to everything else for a moment, etc. Not trying to be precious about where I build houses.