I think the perfect nerf and fix for post plant meta would be make the molly work like the smoke, just letting you live with 1 hp, (but without recovering the hp back obviously). That will force Viper to pick, but will still have all the advantage
It's not just the viper mollies, teams are also using the sova darts, killjoy grenade... There's so much stuff for post plant it makes the game kinda boring