I would not be so sure. The apple indeed transformed into a DF, most likely the slime's one. Yet, it was said more than once that the ability is reborn "somewhere" in the world.
At least, being reborn in the nearest fruit need to be a really new information in OPverse. I mean, why killing users and taking their powers this way is not the MAIN activity in the world?
I think the WG would have ALL strong fruits in the world by now if not. A weak dude with a really good fruit would yet be fodder to a admiral. Having fruits like gura gura, soul soul, logias etc would be the most logical plan for the WG in the past 800 years...
no the most logical plan for the WG in the past 800 years is using the anicent weapons to kill all pirates. what did the WG do there? they hid the anicent weapons and killed anyone who even tried to use them. only recently did the WG decide they should use the ancient weapons to end the age of piracy and that is why they went after robin.
so is it fair to say the WG is not a bunch of brain surgeons? They don't always do the smartest things.
But hold on that isnt fair, aside from waiving this questions away let me give you a real response.
1st- the world is a big place. Doe you think the WG knows where the Lightning fruit is? It is on the moon. ya one of the best fruit in OP is on the moon, and even before then i feel safe saying that no one in the WG knew enel had it on skypiea. what about the rubber fruit before luffy ate it? granted the rubber fruit is a really bad fruit, but shanks put it in a box and didnt care about it. how could anyone know where that one is? Shiki was plotting to destroy the WG, do you think anyone knew where he was hidding with his df? and his df is possibly one of the best in all of OP.
There are a lot of places for fruit users to hide out away from the WG. And look at what happened to DD and co when they heard about the so called ultimate df. DD went for it, the marines went for it, Law and coza went for it, it was a mad dash and the weakest of that group got to it, somehow law and coza made out with the DF even though some of the most powerful people in OP were out of it.
And the WG as powerful as they are, they still use ships the same as every other pirate. we have seen the SH escape from ships. At the end of the day, all a weaker DF user needs to do is get away in a ship. Akainu can be at the helm of a battle ship, but if foxy sails into a horrible storm, the noro fruit just got away.
2nd- The WG already has some of the most powerful DF in all of OP. The wg has a legendary zoan, had the ice fruit, has the magma, and light fruits, they have magellan, they have all the warlords, so the string fruit the shadow fruit, the darkness fruit for a while, the sand fruit for a little. Fuji's stomp fruit. what more could they ask for?
3rd look at their biggest enemies, they don't have the best df. Kiadou has the dragon fruit, a zoan is a zoan even if it lets the user breath fire, still garbage, BM has the soul fruit, a weaker version of the shadow fruit, which the WG had. shanks probably has none, WB had the quake fruit which is an impressive fruit but when the strongest man in the world has it......it isnt worth the struggle to get it...... and BB has the darkness and quake fruit. Out of the WG's biggest enemies only 1 of them has a fruit worth getting.
4th staying on top is hard. Once you get all the DF what do you do with them? do you lock them up and not use them? if you give them to people you run the risk of losing them. give coby a shiny new df, he can have the fire fruit, but Coby is only around captain level in strength, zoro could kill him. sanji could kill him. carbiou may even be able to kill him. so what happens when coby dies with the fruit? now someone else has it. Is the WG really going to devote all their resources to keeping all their marines alive who use DF? or are they only going to give df to adrmial level fighters who they know wont die? well ok but there are only so many admiral level fighters.
And it would take alot of work to maintain this level of dominance. Imagine zoro, mihawk, garp, and shanks all kill DF users on different corners of the world. what are you going to do? dispatch the admirals to all 4 corners of the world? the WG does have a job other then maintaining its DF collection.
5th, why? the WG has a good system right now. anyone can join and they can work their way up to the top however they want to. Garp was able to become the devil for pirates without a DF. I understand that DF objectively make you stronger. but you know what else makes you stronger? getting stronger. What the WG does right now works. If the wg was constantly getting beaten up i could see why the WG would suddenly seak out more DF, but they are still on top and apparently have been for a very long time, and all they had to do was what they are doing now, not stock pile DF.
6th chaos- who knows how these battles really go down. Sure Burgess wearing a backpack on his back filled with apples(and the fact he is a close range fighter) probably helps maintain control of where the DF ends up. but it isn't a sure thing. imagine this- me and you are enemy pirates. I kill your captain the poison fruit user. we are in a heavy storm, your ship is going down, I am poisoned, I need to get back to my ship and leave as soon as i can. I get back to my ship only to find out my bag of apples has a hole in it and the DF fell out. or instead of my bag of apples, when i killed your captain the ship's kitchen was closer so the soul went into a fruit there. Or during the fight you destroyed my bag of apples so i would have to let you live.
7th fighting style- typically when someone gets strong enough asking them to change their fighting style isn't a good idea. Don't forget Franky was offered the fire fruit, that is a logia that is supposed to be good (i say it is mid tier) but he said no. Sometimes someone gets set in their fighting style and they have no reason to take a DF. Zoro really cant use a DF. it would make him stronger, but i doubt he wants to be the most powerful swordsman with the barrier fruit.
and of course....... well..... it just isnt good story telling. do you really want to read a OP where luffy doesnt meet a single other DF user unless they are a WG agent/warlord/marine? Ya maybe oda could make it work with the marines being the only enemies, but then even the SH crew wouldn't have DF users.
I get what you are saying though, I would hunt down df users or at the very least always have fruit on hand. But I really like what Oda did here. waiting till almost the end of OP to show us how DF transfer.