One curious thing is that Max himself didn't seem to think of it as a "healing" power in the beginning. When he's explainig to Liz his powers in Pilot, he said that he could manipulate molecular structures, "That's how I healed you". But that would mean that all hybrids could heal in a somewhat equal measure. Maybe it was until later that Max realized it really was a unique power, like Isabel's dreamwalking.
Well, I'd say rather that the powers that be changed their minds as the show went on. He explains it as molecular manipulation in the pilot because that's how he describes it in the Roswell High books... and in the books they can all do things more or less equally. As the show diversified itself from the books, though, they either forgot that, or changed it.