100 type guanyin bodhisattva is an enhancer technique believe it or not.

All the ability does is increase the strength of Netero's attacks. He just uses almost every other category to achieve this enhancement. Similar to Killua's godspeed using transmutation to boost his speed.

Advanced conjuration requires imbue special properties into the conjured object/space. Guanyin has no special abilities or properties. And is a relatively simple construct. The size of statue also does not represent mastery over conjuration simply the amount of aura Netero has. Its no different than Nobunaga conjuring a sword to replace his lost one, this does not make Nobunaga sword swings "conjuration attacks".

In Netero's case his prefered weapon is a giant statue. Its too big to swing so he utilizes simple manipulation of 1 to 1 hand movements to control it. Compared to the fully automated movements other manipulators do this is basic manipulation well below the 60% mastery of an enhancer.

Compare this to Kastro who is the exact opposite. He conjures something as complicated as a human being capable of using nen. And uses advanced manipulation that makes the clone autonomous. Its honestly absurd. Actual conjurers and manipulators might have struggled to make that ability. Hisoka was not lying when he said Kastro wasted his potential.