Chansey and Blissey's usage wasn't affected by Genesect, imo. In fact Genesect was easy to play against for stall since RP variants are hard-walled by Chansey / Blissey, while the pivot variants are easily worn out by hazards. If anything, the increased usage of Scizor would be annoying for those two.
What really affected the usage of those two special walls are probably the new BW2 addition of power-hitters, namely Sheer Force Landorus, NP Thundurus, mixed Tornadus-T, and Keldeo (not to mention the recent unbanning of Kyurem-B), all of which can power through Blissey / Chansey.
What really affected the usage of those two special walls are probably the new BW2 addition of power-hitters, namely Sheer Force Landorus, NP Thundurus, mixed Tornadus-T, and Keldeo (not to mention the recent unbanning of Kyurem-B), all of which can power through Blissey / Chansey.