I think they sort of agree with you, which is why when you click a five point ability it auto-spends all five points to max that mastery.
The issue, I'm guessing, is that having the system reward you one point for each level you gain, until you are level 30 with 30 mastery points, is very easy for everyone to understand and tally. If they "fixed" it to have only ten points, then it would have to be "+1 mastery point/3 levels". You'd just be trading one mathematically inelegant system mechanic for a different mathematically inelegant system mechanic.