Sliding is not crap. If a defensive line slides as one and in unison it is the single best defence against crisp ball movement or players like Hayne, Barba, Slater, Bowen. 6-8 players can effectively cover 25 metres of horizontal turf if their slide defence is good.
Its a lazy lateral mover or the guy that rushes up that inevitably lets through the line breaks or tries. If the slide defence has trust and works as one unit it's incredible hard to penetrate if all of the line are capable defenders. Sides like Manly of the mid 90's, Roosters of the early 00's and Dragons of the late 00's have all shown mastery of the slide defence and that it wins comps and shit loads of games.
Beau Scott was a part of the second best defensive line of the modern era and certainly played his part in sliding effectively. Sure he is good for a great read and jamming up and smashing someone but he has let tries in that way - none more memorable then the jam up on lockyer in Origin 1 2011. Scott will slide next year, jamming up will be a rarity that hopefully comes off everytime he attempts it.
Sorry for the long rant - but i appreciate a well drilled slide defence. It's all about communication, awareness and balancing instinct against trust. Its certainly not crap. Every team does it and the team that gets it right in september generally wins the comp.