It's completely up to you and you know your work best. Ultimately you have to decide, none of us can do that for you (though when you get to 50 posts, you could post some of your work here for some thoughts).
I will say I'm not entirely sure what you mean by your definition of a chapter. One scene can happen over multiple chapters, and a chapter can also tell one scene. You aren't writing a short story anthology where every chapter needs to have a beginning middle and end in such a structured way. Honestly, there is something to be said about feeling it. About asking yourself, "Does this feel like the end of a chapter to me?"
Also Harry Potter is not the best thing to compare to as by the time Rowling got to the later books she was one of the most popular authors in the world. She could get away with things others of us cannot, and has herself admitted she wished she'd edited Order of the Phoenix better. And honestly, it doesn't exactly serve your argument either because if there's one thing she was rather critiqued for in those later works . . . it's length. For the record, I also write upper MG, and like to stick to the shorter chapters thing. Something else to keep in mind is if you do indeed want to go with longer chapters that is something you are going to have to sell an agent on. So you will, in some ways, have to be even better than say an author with a more average length of chapter for their work because you will be judged more carefully for making that choice. I speak from experience but in a different sense. My first MG was twice as long as the average at 80K. My editor said it was fine it was so long, but because of that we had to be extra diligent that every single word had earned its position because I was writing as an exception not the rule. Also keep in mind you will be querying often the beginning of your work. Sure the chapters might get shorter, but an agent isn't starting off reading those shorter chapters. She's reading the longer ones.
Anyway, these are all things to keep in mind, and not me saying "No, don't do it!"
Make an informed decision, with all the facts, and then go from there. If your chapters do have to be as long as they are then that's what they have to be. And if it works it works. And when something works, agents and editors snap it up.
(one last thing, when you split your chapter in two, you usually can't just literally do it and move on. Usually at least an extra sentence at the end of the first of the two chapters needs to be added to make the ending feel like an end to a chapter, sometimes even a paragraph. Sometimes too at the start of the next one you'll need a little extra as well. Here's an example I just made up.
Original chapter:
"Now that takes us to the next thing."
"What's the next thing?"
"Well next you'll have to fight the dragon in the castle, see . . ."
New split chapter:
"Now that takes us to the next thing."
There was a next thing? Of course. John was getting seriously tired of next things quite frankly. Maybe he wasn't actually ready to be the King's personal body guard after all. He sighed.
"What's the next thing?" he asked, really not looking forward to the answer.
Chapter 2
The old man gave him a wink and leaned in. ""Well next you'll have to fight the dragon in the castle, see . . ."
Or you know, something like that
, hopefully you get my meaning.)