I agree Netero is overrated but i think he was on the royal guard level during his fight against the king, not below. He is overrated however because i've seen people puting him far above them when it's not even certain he is stronger. Pitou(who i believe is the second strongest guard) tanked a hit from his haokusho cannon(strongest attack) with zero damage and despite seeing it for the first time, it caught a glimpse of its movement speed.
It shows that with time, it could have adapt to it exactly like the king and likely counter it. Though it's uncertain of course, but it shows their level weren't as far apart as some people really want to believe. The fact Netero used Zeno to try to seperate the bodyguards tend to prove that. The truth is that he knew he couldn't really defeat the King, so he prepared a safe place for his nuclear bomb. I think Feitan is overrated as well. Same goes for Chrollo at times for people who say for sure that he is stronger than Zeno using an inconclusive statement