AP Rengar is BUSTED!

So, I'm a Rengar main, and ever since the release of the Hextech Protobelt-01 I've been playing AP Rengar just for fun. Well, I thought that it would be awful, and while it's not very effective early on, it's completely broken in the mid and late game. I mean I was LITERALLY one-shotting the enemy AD carry every time I was able to get close to him/her (poor soul). Not to mention I was able to do massive amounts of AoE damage. In all honestly, I find AP Rengar to be even more effective than AD Rengar, because even though AD Rengar is still really powerful, usually he won't be able to one-shot the enemy squishies (unless of course he's fed). Sure, with AP Rengar you have little sustain and little sustained damage, but the burst is just... dirty! I feel like a complete asshole when playing full AP Rengar. I just wanted to see what you guys think about AP Rengar, and I also would like to know if Riot plans on nerfing the AP ratio of Rengar's W, because while the ability does have a relatively low base damage, it does scale with 80% of his AP, which to be honest is a bit of an overkill. Especially considering that he's supposed to be an AD assassin. Another concern of mine is the Protobelt. In my opinion the item is waaaaaay too gold efficient. And just as an FYI, the only reason why I'm posting this is because while it is fun, I think it's really unhealthy in terms of balance, because at the moment there's really no solid counter-play to full AP Rengar as stupid as that may sound.