"How come Todd Ingram didn't kill Scott in the beginning of volume 3? If he can punch a hole in the moon, couldn't he have finished off Scott the moment they met?"
This is attempting to make use of authorial intent to limit a character's strength which generally doesn't fly around here. If you asked most content creators what they thought of the stats on this site: say, Mario being a galaxy-buster: they'd probably laugh at you and tell you that it's silly, as they never intended for such to be the case.
The fact remains that Scott successfully not only (repeatedly) damaged, but drew blood from Todd, meaning he to some degree or another has parity with his physicality: one cannot, after all, "hold back" their durability, and even if they could somehow anyone as reasonably intelligent as Todd would under no notable circumstances do so. A feat remains a feat.
If anything, Scott getting the Power of Love is a good mark in the timeframe of the series demonstrating around when Scott gets his act together and is consistently Todd level and upwards.
To answer the whole "it doesn't make sense for him to jump that high in so short a time", A: This happens all the time in fiction, it makes no more sense there yet it's still considered perfectly valid, and B: It especially makes sense in a world that runs on video game/cartoon logic, in which people do, well, precisely that: achieve an immense increase in strength within a short time period.
P.S. : I know I can't really stop you from doing so, but a personal request? Please don't drag O'Malley into answering Versus Debate questions if possible, I respect the man too much to make him put up with debating what should be a fairly ordinary verse to evaluate. I mean, look at how frustrated Kamiya seems to have gotten since the whole Dante vs Bayo thing.
Content creators have a fairly straight-forward mindset when it comes to their projects and that helps stimulate quality story-telling, we shouldn't try to force them out of it for what ultimately boils down to "Which fictional character can, in my opinion, kick which other fictional character's ass."