Adult Gon is not Gon's true potential
There's a lot of misconceptions surrounding adult Gon form, with many people thinking that it's just him aging himself to get the power he's going to have in his prime as an adult. I think the only thing supporting this theory is Killua arriving to see Gon in that state and wondering how many years of training would it take for him to get to that point. However, that doesn't really confirm that this form can be achieved naturally through normal training, because Killua himself doesn't even give an answer to that question, which may suggest that the answer is too many years for a single person's lifespan. Plus, it's not like Killua knows what Gon did to himself, what pacts he made and at what cost.
I feel like Gon's own statement during the making of the pact is a much more reliable source, and he clearly says that he'll need all the power he'll ever have. So not just one specific instance of himself in the future, but all of it, every last drop. This also makes sense with the drawback of him never being able to use Nen ever again and basically turning into a raisin for the rest of his life if it wasn't for Nanika. This feels like too high of a price for essentially borrowing one day from his future self. To add to that, Nen is established to grow stronger the more restrictions the user places on themselves. With the restriction of never being to use Nen or even live normally again, the Nen's power should skyrocket far beyond what's naturally possible.
Another thing I feel like people forget is that we already have a rough idea of how strong Gon would be when he grows up and reaches his full potential as a Nen user. Of course I'm talking about his deadbeat dad here. I think we hear multiple times throughout the story how Gon is almost 1 for 1 copy of Ging, especially in potential, with them even becoming Hunters at the exact same age. And while Ging is undeniably one of the top Nen users among humans in HxH world, he's still not close to being the strongest, and it's even implied that he's not the strongest Zodiac, who themselves aren't on the same level as Netero. Meanwhile adult Gon's power has reached Meruem's pre-Rose level, which is pretty clearly established to be beyond what any human could even dream of achieving, including Netero. Gon is only stated to be a 1 in 10 million talent by Wing, which is insane, but not like, beyond humanity level insane. We know this isn't even the ceiling of talent for humans because Tsierriednich exists, and I doubt he'll ever become even close to Meruem even after he completes his training.
