I'd say any time someone is engaged and you clear you buddies 6 it is a pick. Here is where the problem comes in.... In a furball fight many times folks are clearing eachother which is not frowned upon. The problem comes about when someone just sits up high and is not involved in the furball but simply drops in trying to score a kill. The latter is a cherry picker IMHO. Kind of like someone getting a medal when they were hiding behind a rock when the rest of the unit was in harms way.
When confronted by a veritable sea of Spit16's, Nikis, Hurris and La7's keeping them at arm's length is precisely what you should do. Most complex engagements in AH are predominantly of that typical composition. To get deeply involved with them is to play "their game". The way to defeat them is to exploit energy and position to negate their numerical and maneuverability advantage. The art of doing that is not something everyone can do with a high degree of proficiency, if everyone could do it proficiently there wouldn't be a sea of Spit16's, Niki's, Hurris and La7s. There'd be a sea of Fw190s, Jugs, Typhoons and Ponies and we'd be playing an entirely different game.
People who are proficient at Cherrypicking are extremely valuable in a complex engagement, they have a force multiplication effect because not only are they destroying enemy fighters, they are saving other friendly fighters from destruction and less likely to be destroyed themselves in the process. So, a cherrypicker is at least twice as impactful in terms of the net effect on the ebb and flow of an air battle as the typical 1 vs. 1 duelist is.