How is Silva on the same league as the royal guards, which arguably one of the weakest ones (Pitou) neg-diff'd Kite? Silva & Zeno struggled with Chrollo as well & we've seen how desperate Zeno himself was to take down Chrollo (willing to risk his own life). Also during that fight, Chrollo had to intentions on killing either Silva/Zeno, he just wanted to steal his abilities and even then he was able to hold his own.
Being the head of the family, Silva should be the strongest current Zoldyck, stronger than Zeno. During the fight against Chrollo, Zeno was the more active fighter, Silva was rather passive. Zeno and Chrollo are in the same league, with Chrollo probably a little stronger as Zeno admitted later as Chrollo was looking to steal his ability rather than kill. Chrollo was just about to be finished off if it wasn't for that phone call from Illumi though. Silva and Chrollo seem to have clashed earlier too and it just seemed like to me that Silva came out on top as he commented that Chrollo has gotten stronger than before. That seems more like a thing someone stronger would say when confronting someone again. But the difference between Chrollo and Silva or RG is minimal anyway.
Btw, Pitou is probably the strongest of the RG and she didn't neg diff Kite. Kite did put up a fight which is why she kept his body to amuse herself with him. Besides, Kite lost an arm even before they got started seriously.