I have no doubt that someone COULD write a lot more than 20k words about the story of 3.5's development, but I don't think an answer of that length (or shorter) would necessarily be so incomplete as to be bad.
When I was writing the question, I imagined an answer might have something like ~4-5 sections, each of which would be something like "The designers didn't expect players to do any real amount of optimization (link to story about the Druid playtester not taking Natural Spell)", "There were a lot of assumptions about how the game would be played still left over from 2nd edition (link t…