What you are missing is that for several weeks prior to the linear hard fork, linearity (or at least a very strong attenuation of n^2) was largely in effect already due to the 'whale experiment'. Whatever gains you are seeing there, to the extent they have any tie to the payouts, would correspond with getting rid of n^2, first by whale voting changes and later by the fork itself.
Also, IIRC one of the forks (I don't remember which one) botched the payout pool logic and resulting in there being hardly any payouts for a month or so. That may also have helped the price, but can hardly an endorsement of n^2, or even paying rewards at all.
RE: HF21: What Makes Steem Valuable?