Vayne isn't getting a Net buff
She's getting power redistributed. She's losing the Crit on Q's bonus damage, and is getting increased percent health damage instead. The health per kill is likely attributed to get the ball rolling on those 1v5's they so enjoy. Double W stack is a bug that's getting fixed.
Changes meaning, she's going to be more effective against Tanks and less so about Squishies, bringing her back as the Tank shredder instead of the General duelist. A buff against Tanks, a nerf against Squishies.