It also provides massive cd reduction for you to use it continuously for ganking, even twice in a fight. Yes, one good ulti is enough for a fight, but massive cd reduction allows you to use it for a second time. Yes, but then what can he contribute post laning phase? He can spread STD with his Skin but that playstyle is too passive. If buying utility items, many other heroes can farm items faster than Viper while is still relevant later on (like Razor, duh). Nethertoxin is too weak for a steroid, kicking in way too late and not efficient.