I always took it to mean they didn’t have the full scope of Toa abilities. Something more akin to a Bohrok.
That said, gravity isn’t the most dynamic elemental force to begin with, so I can’t think of an example that would be Toa exclusive. Like you said, Icarax used gravity to crush the Codrex (making an artificial gravitic point at the center of an object/fixed point in space) and earlier that story year Mutran increased his own personal gravity to keep from being blown away (manipulating the natural gravity of the environment). Honestly, what else can you do?
Using another elemental Makuta power as an example, the Sonics kraata power permits vibration and raw sonic output, even forming creatures out of sound, but specifically prohibits fine control of the sounds made:
Krakua, alternatively, could probably play a ventriloquist act by having his voice emanate from an object across the battlefield, while at the same time being unable to create a sonic creature. I think that example has clearer distinctions than gravity; gravity is likely just a difference of precision and overall power. Perhaps a Toa of Gravity could have had the Codrex crushed already. Justy thoughts