I really do not see it like that.
So far, in HxH, we were shown that quality of training and quality of the person training is far more important than how long you are training.
Zochi for example trained a long time under wing but still didnt manage to even compar to Killuah and Gon who, through intensive training for a short time, got to a decent level of nen mastery just because they are a) geniusses and b) dared to take that intensive training.
Ging is a genius, much like gon, there is no reason to think that ging trained excessively to get as good as he his, because gon didnt need to, either.
Gon had three times in his life in which he actually trained in a way which gave him a power boost:
Heaven's arena, greed Island with Biscuit and chimera ant arc with biscuit.
All of those were rather short interludes and had a high pay off.
The rest of his skills were learned along the way by observing (for example high zeguzerra was able to jump so high).
We know that Killuah and Gon do train there muscles to some extent (they were in a gym in the chimera ant arc) but it is never implied that this training does anything more than just keep their high level of general fitness.
Still, gon grew excessively in strength (just as killuah) in that time despite still being young.
Why would it be unreasonable to assume that ging didnt traing very hard to get where he is?
Ging is not very intersted in fighting, he is interested in aquiring knowledge and finding things.
He is able to learn insanely fast from others to the point at which he is able to even copy their nen, but that could aswell be a talent he always had to some extent (we are talking about a manga here in which persons are born with the talent to foresee the future, so it is not imporbable).
Still, ging is just a normal human being.
Even Netero was just a normal human being, he was fragile as a human being and the thing really amazing about him was his hatsu.
His amount of nen was impressive, too, but this was not the important thing.
The Hatsu was only aquired by getting so far in his training that he had time to pray for days and weeks and empty his mind.
This is something unique to netero and nothing someone else can just copy.
The only thing don freeks could possibly do to get stronger is nonstop basic nen training like gon and killuah did in the chimera ants arc.
But they had help from biscuit and were absolutely beaten after each training unit.
If Don would undergo this excessive training, he would be on the DC helplessly because he trained himself to exhaustion which would probably get him killed.
Furthermore, you assume that you have to be crazy strong to survive the DC alone and even netero had problems doing so.
That is not fully true. Netero left because it was not the challenge he searched for, not because he couldnt handle it strengthwise.
Even teams of normal human beings got far enouguh on the DC to at least get to the ancient items.
The problems were the calamities, essentially deathtraps, which got them killed.
Don freeks could be as strong as he wants, he could not survive a one hit KO like alluka's ability.
The whole point of him is that he is the human with most knowledge about the DC so that he can even write a book about it (or two).
The DC is VERY huge, it dwarfs our world. He only had less than 300 years to write the book about one side of that.
If you had found a very dangerous continent which is much bigger than our earth, exploring one whole half of it in 300 years and writing a book about it does not even leave you much time for training.
I stand by more word, the only thing which could possibly make DOn freeks more powerful than humans like netero would be that he can use items on the DC which for example make his Nen 10 times more powerful for some time or something like that.
But his basic strength without stuff like that wont exceed netero, leave alone meruem.
The thing with umans is that they have a strength cap as it seems in HxH.
Meruem was so insanely powerful because he didnt have one (at least we didnt get to see it, he grew more powerful by the hour).
If the King of ants can get to the level of post nuke meruem in less than a year, i really do not see why Don freeks should even attempt to train if there are chimera ants arround which are older than meruem and beings even more powerful than that like the calamities.
It makes no sense, he wont outtrain them even if he trains for 1000 years.
There have to be possiblities only he discovered to get by in the DC without being superman.