The point of the fight against Kuma was to show them that they really weren't strong enough.
They HAD to get stronger, to even survive (so, imagine how strong they need to become if the aim for the top).
If you don't get it I will help you to understand why SH lost on SA. Its a joke to call it fight at all, since they lost to Kumas and Kizarus teleport abilitys. Logically speaking the SH should the next battle even if Luffy learned Haki and to predict how the enemy move, since even if he can follow the "teleport speed" he can't fight against Kizaru and Kuma at once, if they split up and attack his crew one by one.
But I get the feeling its senseless to explain it to you since it appears you would be happy to see a "Getsuga Bleach" like Luffy who can split the earth in 2 if he likes to.
@Josl: About the SN, sure they will train in the New World, but you don't get my point. It can't be compared since their fights can't be compared with the the training the SHs get.
Luffy get trained get Trained by maybe the strongest man in the world (at least up to this point).
Zoro gets his training from the world best Swordsman.
Nami the Navigator gets her Training at Weatheria the best place to learn how to navigate on the sea.
Usopp - To be honest I don't know what kind of training he can get, besides how to fight for himself and not counting on others all the time, since Herculas may be strong but his "help" is as worse if the enemy himself.
Sanji learns too fight on the level of an RA Admiral.
Chopper lands on "Medical Ohara"
Robin works with the RA an Underground organization for information gathering.
Franky the Engineer found Vegapunks Labor an Blueprints.
So half of the SH is getting their training in the best possible environment.
Back what I said in my previous post. If SH still can be compared with the SN in the New World, than it only means the SHs are stupid like hell.