I think the skill is in figuring out what each individual likes. Some like very firm suction, others not so much, some like a lot of tongue action and some hate it. Just depends. Same goes for playing with the balls, some can't stand to have them touched at all and others can't get off without a little attention there too.
I look at it the same as going down on a girl, a guy can be down there for an hour but if he's not hitting just the right spot then he might as well not even bother! Just because it got another girl off in 2 seconds doesn't mean it's doing anything for me.