We see all the time in fanfic Harry going all "I need to learn some big choclately spell and then gain all the magic power so I can win". A stunning spell or disarming spell still takes out Voldemort. Harry's strategy in the books was actually good. His only weakness really was an inability to kill but he is literally still a child by the end. Like, Harry could beat Dumbledore or Voldemort in a fight by just being confident, and fast with his wand and his feet. Cool spells are better for showing off or not one on one battle reasons. Honestly Voldemort could have just as easily died from someone hitting him with a stray killing curse or some shrapnel. That is actually a funny concept for a fic ending lol. Just, mid speech a piece of shrapnel from a fight off the ways flies into his skull.