The journey of the Straw Hat Pirates across various regions in One Piece is always fraught with countless dangers. Frequently, the members of the Straw Hat crew find themselves entwined in fierce battles for survival. They must fight against the Navy, other pirate crews, or even the perilous waters of the Grand Line itself.
During the timeskip, each member of the Straw Hat Pirates was sent to a different island, where they honed their skills to prepare for their journey into the New World. However, since each island presents different challenges, some members faced far more perilous conditions than others. Some even had to endure a “brutal training regime” that pushed them to their limits after overcoming the trials set before them.
Each member of the Straw Hat Pirates trained on different islands to enhance their skills during the 2-year timeskip
Each member of the Straw Hat Pirates was sent by Bartholomew Kuma to an island best suited for their training needs. Luffy was sent to Rusukaina, a dangerous island located near Amazon Lily. Zoro was sent to Kuraigana, the home of the legendary swordsman Dracule Mihawk. Nami was sent to Weatheria, a peaceful island inhabited by a group of weather scientists. Usopp was sent to Boin Island, where he encountered a series of dangerous creatures.

Sanji was sent to Kamabakka, the island home of Ivankov. Chopper found himself on Torino Island, an island populated by a mix of humans and talking animals. Robin was sent to Tequila Wolf, an island where a group of workers had to build a massive bridge. Franky was sent to Karkuri Island, the home of scientist Vegapunk. Finally, Brook ended up on Namakura Island, where he encountered a group of religious priests.
The islands may not be easy, but they are well-suited for each member

As we can see, most of the Straw Hat Pirates, including Nami, Brook, Franky, Sanji, Chopper, and Zoro, were sent to islands that posed significant threats to their survival. Notably, Nami and Sanji had a particularly difficult time with the local inhabitants, although Sanji managed to charm his way through most of the encounters. Meanwhile, Brook, Franky, Chopper, and Zoro faced several challenges while on their respective islands, primarily battling dangerous creatures while quickly adapting to their new environments.
As for Robin, despite facing the harsh conditions of her journey, including fighting against the oppressive laborers of Tequila Wolf, she eventually found herself among the Revolutionary Army. Although she faced numerous threats along the way, she also discovered a safe place to rest and strengthen her resolve.
Luffy and Usopp faced incredibly dangerous islands

While Luffy’s island is known for its strong creatures, Usopp’s island was specifically chosen for its rigorous training conditions during the 2-year timeskip. On his island, Luffy also received help from one of the strongest characters still alive in the One Piece universe, the Dark King Silvers Rayleigh. In contrast, Usopp had to survive on an island filled with dangers, while still being one of the most beloved members of the Straw Hat crew.
Although he had the assistance of Heracles, who guided him through the training, Usopp had to muster all his strength to survive, as he faced many close encounters with death on that island.
If Luffy, Zoro, or any other Straw Hat member were sent to Boin Island, they would likely have a much easier time surviving than Usopp. However, for one of the most beloved characters in One Piece, this was a fierce battle for survival.