I have my own thought on midichlorians: Qui-Gon was wrong. No big conspiracy or anything. He was just in-universe misinformed, such that cause and effect were reversed.
You're not strong in the Force because you have midichlorians. If that were the case General Grievous's attempt to become Force sensitive by infusing the blood of Syfo Dias would've worked.
You have a lot of midichlorians because you're strong in the Force, and they're drawn to that like flies.
It's still a useful measure, but there's no causal element to them.