Lethality is broken on Vayne or any AD Champion that has stealth.

So I just went against a Vayne who was rushing Duskblade and can I tell you how broken that it? Right after she got that item, combine with her tumble and ult she does a total 800 flat AD damage and not to mention that lethality gives her like 16 armor pen. I'm sure that all the patches had been through the PBE, if so then how did this get leaked through to the public on patch 7.14? It's like broken so please, fix this there has been too many bugs with your game. Hire more bug fixers man.