Just to check, I went to BS01 gravity page and I didn't find anything claiming that gravity one of the rarer elements.
However upon checking the powers that gravity Toa have, I could well understand the GB going easy on the Gravity Element.
For example Hewkii, just with the mask of gravity, lifted the Coliseum off the ground long enough for the Hagah to get under it. Even
though the Hewkii passed out, the Coliseum is still a massive building. I can see why the GB would be careful making to many of
beings with such power.
"The invasion of the universe core is proceeding well, my newest creations are spreading darkness and corruption, and in general, it is good to be alive."
— Mutran, The Mutran Chronicles
"And you still haven't answered any of my one-hundred ten questions, or my follow ups."
— Vezon to Trinuma, Destiny War
"Another Hafu original!"
— Hafu, Mata Nui Online Game
The biggest sacrifice in bionicle. Its a tie between Matoro giving up his life to save the universe and Hafu knocking down his beloved pieces of nostalgia to save Po-Koro.