[Esuohlim]

The bomb was a red herring. It caused the incident they were trying to prevent, so there was never ever a split in the timeline. The underwater island was a symbol to show that it was inconsequential to getting everyone together in the end during the whole bullshit purgatory epilogue.

Everything make sense when the flash-sideways is perceived as completely fake, even the cheesy stuff like Sawyer and Miles being partners-in-crime, but that still doesn't mean it wasn't completely stupid