But if toriel wasn't in the start the human would have lost

Yeah but Flowey has had assistance with the souls

Does flowey count? He doesnt have hands.

I guess but what else in the underground can kill the human with their hands behind their back

Not really, like the game says he is the weakest, papyrus can defeat sans, people only think sans is the most powerful monster because of his boss fight, sans only has 20 dodges (yes i counted) and papyrus can drain those without breaking a sweat.

also about karma, that only works when somebody has killed people, so sans can only deal 1 damage per attack.