I think this fits perfectly because of a theory of mine. Star Platinum's bullshit abilities make more sense if his ability isn't The World, but mimicry.
It takes the form and face of Jotaro, has the same range as Magician's Red and only manifests after Jotaro witnesses it, can enter his own and other's bodies to control them like Hierophant Green, though less painfully, gains Star Finger after witnessing Silver Chariot's sword counterbalancing it's range, and only mimic's Dio's abilities after seeing them: flying during Kakyoin's fight, seeing in stopped time after learning of it, and even mimicking Over Heaven's Truth.
I think the main reason Jotaro seems to drop abilities and get nerfed from time to time is his relatively average developmental potential, meaning it takes more effort to maintain needless abilities, hence dropping durability, phasing into bodies, and Star Finger over time.
By taking this observation and mimicry method to it's logical extreme, and as you said, Jotaro's intrinsic desire to improve and protect, he would definitely gain the ability to copy and near-match anything and everything around him.