Alright, I'll make this quick because I'm going to leave to work on my chem lab report(RAAAAGE) after this.
Marth, when shined from on the stage to offstage(supposing no ledge grab) has a much stronger chance of making it back than Ganon does because his Fair covers all of the area Fox could edgeguard from when he DJs until when Marth grabs the edge. Unless Fox waveshines Marth offstage then grabs the edge he's not usually going to kill Marth.
If Marth is shined offstage with his second jump still he can use DB stalls to wait out Fox's invincibility(usually) and return safely.
Ganon, because he has a slower up-B(with some startup time), can get shined out of his recovery with ease. If Ganon is shine with a second jump but too far away to DJ Uair(his only hope of smacking Fox away so he can recover), then he will get Bair'd until 1. he is forced to wizard's foot. this will result in a ledge drop shine spike or 2. an early shine to ledge grab by fox which works faster. Both have room to screw up, but the Bair guard is typically used among higher level players so I guess it's more reliable.