I know this would never happen, because they are all great friends, but hypothetically, if such a duel were to ever occur, would Harry alone be able to defeat Ron and Hermione together? It’s a terrible thought, but I am really curious to see what others have to say about this matter.
Remember, Harry taught the DA, was consistently the best student year in and year out in DADA, was the only member of the DA to be neither injured nor incapacitated in any way, shape or form during the battle at the DoM, could hold his own against even the most formidable Death Eaters and escaped from Voldemort on several different occasions, and eventually brought about the Dark Lord’s downfall. Harry was also one of the only wizards noted for being able to resist the Imperius curse, and could conjure a Patronus in his third year, which was virtually unheard of for a student of his age. He was also able to produce Unforgivable Curses as well as the lethal Sectumsempra, skills which as noted by Severus Snape, take a great deal of talent in the ways of the Dark Arts in order to achieve.
It is pretty evident that Harry is the most naturally powerful of the trio, but would that be enough to take both Ron and Hermione fighting together against him in a duel? I don’t think anyone here would disagree that Harry could beat either Ron or Hermione separately in a one-on-one duel, but could he take them both at the same time?