I find it funny how you preface your argument with a comment about thinking ability and then fail on that very front.
They quite clearly state that the problem with a cap is it "inherently feels like more of an expected quota". Your solution does not solve the problem. It actually makes the problem worse, because now, if you happen to fall behind, you're constantly going to feel like you need to catch up to your expected quota.
Because they result in two totally different outcomes.
The system they implemented allows people who are prepared to put in constant effort every week to open up a gap of 2-4 traits over more casual players. The system you propose will result in everyone having to put in the same amount of effort and everyone having exactly the same result.
The great thing about this system is that an individual can choose what is most appropriate for themselves: Aim to get the power first, but with a significantly greater amount of effort, or get the power later with a lot less total effort.
At best you're a pot and Blizzard is a kettle. The difference is Blizzard are using an electric stove....