Gengar is fine where it is. Best offensive spinblocker and a great offensive Pokemon in general are what he has going for it, and he is good at both. He is also versatile enough to get rid of counters with small moveset changes, which just adds to the level of danger Gengar poses to any team. For example, while usually SpD Jirachi and SpD Hippo wall Gengar and are some of its best counters, WoW leaves them crippled for the rest of the game and makes them much easier to wear down. Gengar can fit WoW on either a SubWisp set or on all out attacking set, as with perfect neutral coverage with just two moves, he has plenty of slots to use unconventional moves. Taunt is in the same boat and completely shuts down the blobs, as well as Hippowdon, which once again, are some of the best answers to Gengar. Some other semi-rare moves that help Gengar get past usual checks and counters and are effective are Destinty Bond and Trick (the latter obviously on a Choice set). While Gengar is not the strongest Pokemon around, it deserves its ranking thanks to the utility it brings to a team, mainly important immunities/resistances and spinblocking ability, its good neutral coverage which makes it hard to outright wall, great Speed, and lastly good versatility.