Jumping on bars and cutting the track is an obvious strat and should no considered SC, since even a newbie do it in a lot of circuit.
My opinion is that a SC involves Lakitu or a glitch like turning around the start line or getting a lap count in some other way.
As for SG, the jump is a big time saving but it's not a glitch, it's only a standard very long jump.
The real problem with SG "SC" is that is so hard that can be performed only by luck (that's my case

) or by a superplayer.
In case of luck it's a bit unfair to give a WR for simply be lucky, but maybe this is a problem related at any game/sport.
Moreover I dont intend try the SG "SC" again, and the only time i got, i taked, after landing, the wrong way...