You're saying this as if I'm not one of the Millennials who was caught up in Pottermania. I'm aware that it had a huge influence, but that momentum of that influence has been tempered by some pretty bad blood spilt between Rowling and her fanbase, which has caused a lot of fan reflection into the prior toxic elements of the established fiction. People aren't really talking about Harry Potter anymore except in terms of "I didn't know there's another Fantastic Beasts movie?" and "WTF has Rowling done this time?!" But we're not really seeing the things we once did either with anywhere close to the prevalence it once had: e.g., Patronus or House quizzes. It's a lot like Game of Thrones. It was once the highest rated show, but who's actually talking about it anymore?
Many of those YA fantasy series have already come and gone. And if it's in the next decade, it's definitely not today as per the original prompt.
I could see the influence in terms of determining the schools of magic, but simply casting at-will magic using wands was quite prevalent before and after the Potterverse.
Re: future YA series. Yes I am aware that the past, present and future are, to my puny human mind, different things. Thanks.

My point is that the influence is continuing and will continue, no matter how naughty JKR is.
It's not at all like GoT. GoT has just vanished, and will eventually creep back in as people who skipped it see it, people who saw it go back and re-see it, and as spin-off series emerge. Re-appraisal will be kinder to it. The first few seasons are extremely strong, and when people come at the final two without the same emotion and same surprise at the crap-ness
Potter is, as you say, on the way out. It's not coming back. But it's huge. It's been huge for two decades. There's no way writers would have avoided the influence, and if the game was created the same way as D&D, there's no way there wouldn't be a class which was clearly Potter-influenced (because with D&D the players heavily influenced what classes existed). It's not just casting spells with wands, it's the sorts of spells that are cast, how they're cast, how they're named, what a wizard is, and so on. And yeah some of the stuff that's already come and gone has been influenced and that's going to keep happening. But it hasn't vanished like GoT has, sunk without a trace. In fact every time JKR decides to spice things up, or some game or film studio decides to make a Harry Potter game/film/show, there's a giant discussion about it, and loads of people still like it, and just don't want to give money to it, and so on. People talk about how they're saving their books to give to their kids so they don't have to buy new ones and fund her - but the point is, they're saving their books. Whereas GoT prequel stuff? People just mostly ignore it. Not even a real discussion.
I obviously agree it's hardly a horribly original style!

I'm not gonna argue with that! Yeah she's just a more famous proponent of it, but either way you end up in the same place!