Colors seem to be more popular than they used to be.....I like the fact that they are, actually.
Anyway, the only way Gengar really wins against anything is if it flips a lot of heads on its Power. Poltergist is still easy to play around, and even if you do Trainer Lock me, you're still dealing 0 damage, while I smack you for anywhere from 60 to 120. (The exact number depends on the deck)
You also can't Trainer lock for ever, The turn after you use Poltergist, I'll gladly burn all my Trainers and play all my Skull Fossils in my hand. Then what are you going to do next turn?
SPs are a nightmare for Gengar, especially against Toxicroak G. Poltergist is the only thing that will truly harm me, and even then, I'll laugh why you deal 0, yet you're getting 10 from Poison (I can put in Skuntank G in any SP deck, just for Special Condition benefits) every single turn in between turns. Sorry, but Gengar fails. Especially against Toxitank, the main SP deck.