I know they've lumped Quintessence/Power Cosmic under Cosmic Energy. However, is there an official errata for all figures calling for Quintessence or Power Cosmic in text on abilities like:

DEATH TO THE GUARDIANS: Sinestro can use Pulse Wave. Opposing characters that can use the Quintessence team ability instead can't use it and modify their combat values by -1.

No. The specific team abilities still have their own names. Although Quintessence, Power Cosmic, Cosmic Energy, and the Q Continuum all DO the same things, they are not the same team ability for things like this.

Wow thats very silly. Guess thats gonna be my favorite new house rule.

Avengers and JLA abilities work the same for long period of time and I wouldn't find it weird if an wffect only worked ob the JLA and not the Avengers or vice versa.

Its less of that and more of a legacy figures not working with new figures. For instance, as written, that special power would never trigger on any new figures since Quintessence seems to be a retired phrase replaced by Cosmic Energy.