@John:
Besides Luffy using gear4, we haven't seen much. And it's been 5years since the eclipse….
Yeah, we haven't seen much, we've only seen Zoro drastically improve his swordsmanship and gain Buso Haki, Sanji being able to easily do moves that hurt him before (plus Sky Walk) and gain two forms of Haki, Nami's control of the weather increasing, Usopp's Pop Greens and Observation Haki, Chopper being able to control his Monster Point form (and becoming much more of a bruiser), Franky gaining a ton of new weapons and the Franky Shogun, and Brook considerably improving his swordsmanship as well as honing his DF ability.
There is the Robin case though http://www.mangareader.net/one-piece/773/5
Oda created the most OP DF, she could have wrecked the CP9 by herself easily and could beat every SHs but Luffy ( cause, he's rubber you know, so she can't break his bones or what ).
The CP9 were all highly trained and skilled warriors, you really think they would fall that easily to just Robin? Her extra limbs can be harmed, which will affect her.
Yes, everyone was fine at the firman island, but that was just "hey, let's show how the SHs are super strong after 2 years but not really". Common, Jinbei could have dealt with this situation alone without any single help.
the whole Hody thing was so lame that Oda decided to kill them….....
Jinbe could have beaten 100,000 Fishman warriors by himself? Yeah, no. The point of the Fishman Island arc was to show how strong the Straw Hats were after their training, with special emphasis on the final battle being won as a result of the new abilities the Straw Hats have gained. Had they not trained, the battle would have been much closer. Caesar would have then without a doubt killed everyone on Punk Hazard. Doflamingo would be completely out of the question.
–- Update From New Post Merge ---
No one complained about Luffy struggling in the Grand Line despite his ten year training at home