So John was perfectly willing to let a little girl die?

Jigsaw's methodology is really just deluded belief. He's simply pissed about the way his life went down the drain and is taking it out on random people who has sinned in some way. He's forced his test subjects to murder mutiple times in the franchise and has used pawns for the sole purpose of other victims and sees all crimes as equal. He doesn't understand the true psychology of his nature and ways which makes him defy his own standards. Gordon's family are merely pawns to reflect his sin of supposedly having an affair.

Hmm... I can justify this buttttt

Something tells me you havent watched the whole series.

Don't over-analyse the Saw movies.

Also wondering what Zep did to deserve that game. In the brief moment we see him earlier in the movie, he's kind. Essentially pointing out that John is a person, not just some specimen laying in a hospital bed to be learned from. Obviously John is the world's greatest detective and probably dug up some sort of dirt on him, but we never hear what it is. The game he is chosen to play is particularly cruel in killing a child. Maybe John thought he didn't have it in him. Either way, he's basically set up to be the fall guy, which really doesn't seem like something John's methodology would align with. That whole subplot just asks more questions than it answers, for sure.