It still is dependant on your commitment to learn. That's why they do Midi tests in the first place, because they are trying to test beings before they would even have half a chance to understand and use the Force.

Now, with the Midichlorian concept all beings have an innate ability, not just Jedi.

So if anything, Midichlorians upholds what you would like the Force concept to be, whereas without them, you had to be related to someone strong in the Force.

As far as how Palpy avoided the Midi Test, he is a Sith Lord in hiding. Sith wouldn't be taking their babies in for Republic testing, because that would give them away as Force sensitives.