Quite how you think it takes skill to press a button and gain 75bhp to pass in a straightline is beyond me.
Alonso made an amateur mistake, nothing to do with skill to pull off a move.
To press a button on an empty straight, while not overtaking, takes little skill. However, to press a button at the right time, to judge the speed of your own car, to judge the speed of your opponents car, to ensure that you brake early enough for the next corner and position your car correctly for the entire move takes immense skill. On that occasion, Alonso screwed up. And if Alonso (who has the reputation of being the best driver in F1) can screw up, ANYBODY can screw up. The fact that he did screw up, also tells me that there is a high level of skill required to use the KERS/DRS devices when overtaking cars.
The reason why Alonso made the mistake is because there was a degree of skill required to do what he was doing. Had there been no skill required, he would not have made a mistake.
Maybe red bull didn't want to use the extra fuel burn at that stage of the race when they would simply be running more stops and using clear air later to leave him for dust.
The fact that Alonso was later lapped in that race tells me that Vettel could've gone much faster while he was following Alonso. The problem is that overtaking Alonso is not easy, unless you have a tyre advantage. Notice that when all cars have equal tyres, there are very few overtakes...even with DRS. The overtakes for example that we see Vettel doing are invariably when he has much better tyres than his opponent. When his opponent has equal tyres, even with DRS, he struggles to overtake. Bear in mind that I'm using Vettel is an example here. I could've replaced Vettel's name with almost any other driver's (except Hamilton).
DRS does assist with an overtake, but is far from a push to pass button.