Looking at offensive stats, Kobe posted merely solid efficiency on a ton of volume. Look at career PER: 23.2 and 22.8 for Kobe and KG respectively. In contrast a truly game-changing offensive player is Lebron, whose career PER is 27.7 (!!). The difference isn't due to Lebron being still in his prime; he has been more efficient his whole career than Kobe was even at his peak.
That is to say, Kobe was a great offensive player, but not a LBJ or MJ-level offensive dynamo. KG was also a great offensive player, and he changed the power forward position with his shooting, but he was never as much of a volume scorer as Kobe.
Defensively, on the other hand, is where you see a BIG difference. Bryant actually has a negative defensive BPM for his career, which probably undersells him a bit, but the fact is that he is hardly a dominant force on this end. KG on the other hand, well, we've all watched him play: no stats needed. We're talking about the difference between a roughly average defender and perhaps the GOAT.
I'll take KG.
With you 100% until that GOAT part. Certainly one of the greats, but is he really in the conversation for greatest?
GOAT in terms of defense. I'm still not on board 110% with it but I think you could make a pretty strong argument for Garnett's place in someone's top whatever defenders of all time list.
Everyone likes a good list-- so who's on it... let's see. Certainly Russell, Hakeem, Duncan, Rodman, Wallace among bigs. Mutombo, Mourning, Robinson, maybe. Garnett fits in with those guys for sure. Among wings, Pippen, Bowen, and Jordan stand way out, but I'm not sure who else is on that list because wing defense is so different between eras (I might make the argument that most of the best all-time wing defenders are playing right now). At the point, the candidates are probably Kidd, Payton, and Robertson.
Comparing apples to apples, I wouldn't seriously entertain the idea that Garnett surpassed Hakeem or Russell, so the GOAT thing is a non-starter. I can certainly see him making your top-10 list, though.