I have doubts on if Hyogoro will simply be able to gather all the Samurai without problem. Even with his experience, he lacks the strength or resources his old position provided him. At best, I see him gathering one hard to find member, with him instructing Raizou and Kawamatsu on how to find the other members.
Luffy's prison training was indeed bs. The fact he can move around and fight to a fair degree compared to being completely drained as recently as Punk Hazard is a major inconsistency, so having him suddenly become so resistant and getting even stronger from it is absurd. Considering what we've been lead to believe, him surviving harsh battles against Katakuri and Kaido, whilst cheap, would've been a far more consistent way to justify any sudden power up.