The comic at 2:50 makes no sense. Flowey's determination surpasses yours at that point. He controls the timeline, and has the power to save and load, a power he uses to its full advantage (i.e. save states) in his boss fight. When he kills you, he just loads his save so he can do it again. You (Frisk) are not in control
Actually, that depends on when you Die. Only at the end does he abuse Save States to keep killing you. His determination may Exceed Frisks at the time, but if you actually Die in that fight, then he's still relying on you, The Player, to restart the game before he can do it again.
Also, these two are siblings. Assuming Flowey is somehow re-re born at the end of True Pacifist, and Frisk choses to stay with Toriel. That means they're brother and sister. That makes all this a lot more plausible.
Even if he isn't reborn, they still kinda are siblings.