The thing about SP decks is that they indeed CAN take skill at times. In other situations, however, they operate with such an advantage that misplay after misplay can be made and it won't change the outcome of the game. Some of the most basic maneuvers an SP player can make (Dragon Rushing a benched threat, Power Spraying Uxie, completely healing a damaged Dialga) have drastic effects on the outcome of the game. These are no-brainer plays, but they can absolutely break a non-SP player. I played Regigigas at a City Championship one time and on two occasions had my Uxie Power Sprayed. I lost those games because of that simple play, something that any decent player would do (as well as most downright bad ones).
In a format that largely feels like a giant game of Paper, Rock, Scissors (that is, matchups are important), SP's contain the lowest amount of risk simply because of these game-breaking plays. Having a Gloom knocked out by a player's 2nd turn Garchomp X w/DCE is game-breaking, no matter how you look at it. Missing out on a 6-card draw because an opponent Power Sprayed your Uxie is, again, game-breaking. Decks currently run multiple Seeker or Trainer lock to deal with it, but you can't deal with it if you can't draw into those cards.
The worst part is that this does have a lot to do with opening hands or cards drawn off an Uxie drop. I lost a game at NC States playing Gyarados against Dialgachomp. My opponent opened with 2 Power Spray and drew a third one as a prize, effectively cancelling out my first 3 Uxie drops. I was nearly able to win that game, but the early game disruption was too much for me to handle. I found myself passing for a few turns and sacrificing Pokemon until I topdecked something. This is not an uncommon story for people to hear. It happens all the time (as does donks). Is it really skill when a single, obvious play almost entirely dictates the outcome of the game? Also, note that SP decks feature many of these game-breaking plays, so that if a player failed to draw the Power Spray they needed to halt the opponent's Uxie, they still may win simply because they were able to snipe/Bright Look the bench so much that they completely destroyed the opponent's setup.
Keep in mind that this also applies to Gardevoir/Gallade back in the day. GG players could Psychic Lock for the entire game and easily win, completely denying an opponent a chance to set up. Or, if a threat did arise, they could one shot it with Gallade and a Scramble Energy. This only lasted for a year, however, and GG took considerably more skill to play than SP (especially in the mirror) since it didn't really win off donks.