First off, you're welcome, Prawn
As XelNya stated, tier points might have become outdated as a ranking system when the skill rating algorithm was released. However, I don't think they've become completely obsolete, because they were indeed "hand-picked with love" as you stated. Since the intention of the tier point system was to have X tier points on a song be similar in difficulty on every song, and the skill rating algorithm in its current form does not reflect this, perhaps the tier points can be used as a kind of calibration tool for the skill rating algorithm, as I have attempted to do.
That being said, my new formula is far from flawless. Calibrating by tier points has an inherent flaw--there is no hard calibration data below difficulty 50, and only superficial data above difficulty 90. Therefore, extensive extrapolation is required to make the formula reach all songs, which inevitably results in errors. My formula's accuracy starts to degrade below 45, and completely falls apart below 30, in the near-AAA scores. (For instance, a 10g on a 15 would be ranked under my formula as a 14.5, which is ridiculous.)
I could try tinkering with the constants, but this clearly needs additional work before it can become a true upgrade to the formula.