After seeing that needle, I really think Killua should kick his older brother's ass whenever he goes back home. That douche really deserves a lesson he wouldn't soon forget.

But yeah, Rammot getting defeated so easily after Killua got rid of the artificial restriction was natural. Rammot has probably zilch proper nen training and very little any training at all. He has spent his time killing ordinary civilians and horses. The first time he fought against someone worth anything he got defeated very quickly. It's not like awakening nen would be any huge power boost if you haven't got a clue what to do with it.