Let's hear it...Same with Misty already in Kanto she showed to have predispositions to come further than average trainer is able to do in meantime showing bigger improvement
Battling with different types... much like Ash, Brock, May, Dawn, Gary, Casey, Harrison, Morrison, Tyson, Katie, Paul, Barry, Conway, Nando... list goes endlessly on. That Misty is able to battle with different types makes her the same as pretty much every other trainer...showing knowledge of how to use properly other type of pokemon in battle beside water
Again, every character has won or performed well in mini-tournaments like that, some of them more pretigious than the Whirl Cup. Like Ash with the Orange League, the Battle Frontier, the Hearthome Tag Team competition (In which Dawn was a finalist), the Twinleaf Festival, two Pokéringer competitions, etc.Like winning Princess festival on first try, coming top 8 in prestige water tournament(Whirl cup)on first try
Which again, we've seen trainers do for years on the show, most notably Ash, Dawn, May, various Gym Leaders who are specifically prepared to counter types against which they are weak.she managed to learn how to overcome disadvantage when her own pokemon are in inferior position being able to beat Andreas and his Poliwrath who were champions of Seaking contest for years.
And yet, all of was seen in many other trainers... As I said before, the question at the top of this thread is somewhat pointless in that technically, Misty or any other character has a chance of becoming an Elite 4 member, the real question is: Is there something about Misty that makes her a likelier candidate, to the point where it is probable that this will be the road the writers will take with her character should she ever appear again?. The answer is no.All of this are qualities of skilled and great trainer since it ensures that he gains his own pokemon thrust showing being able to adapt to any hard situation in which its pokemon are put into finding best solution to counter it.