User blog comment:Martialmaniac/Zoldyck power ranking/@comment-14902757-20151014211554/@comment-4828844-20151015101231

Yes, I agree with both of you. I like to think that Killua's training style is more inclined in battle, which is why he was late in learning Nen. Silva and Illumi perhaps wanted Killua to perfect everything before proceeding to teach Nen.