Thing is, if Gamma Knife had a huge impact:
- Why did Counter Shock which was applied after Gamma knife not worsen Joker's conditoin, it was used shortly after.
- Why wasn't he at least coughing blood through-out his fight with Luffy? an attack that eats up one's internals should be showing visible signs of detoriation.
- Why are Joker's internal organs intact if his organs are only being held by strings? He's chained in Kairoseki, it should be impossible to use his abilities.
Because none of these occur, it means the Gamma Knife was a short-lived attack that simply required first aid, or Joker would have been in a worse condition.
The time that elapsed from Gamma knife to Luffy using Gear 4th couldn't have spanned no longer than 5-10 minutes, Joker was defeated 30 minutes after Gear 4th; if Gamma knife were so severe, 40 minutes of constant fighting should not be enough time for such a fatal injury to heal except it really wasn't that life-threatening.
Also, concerning any help that Luffy got; under the premise that Gamma Knife was not that effective, Law's main role was leveling the situation (
defeating Trebol) to make it a 1on1 situation for Luffy against Joker.
Once Luffy used Gear 4th, Joker stalled because he knew Luffy was straining himself. As a result of stalling, Luffy needed 10 minutes to recover and help from the colosseum fighters; it does make up for Joker's underhanded tactic imo.
Joker stalled and had been barricading himself with strings in order to avoid getting into a hand to hand fight with Luffy.
The panel above even shows Luffy scream at Joker's strings to
"get out his way"; that virtually proves that Joker was stalling, or Luffy really shouldn't be saying that.
Luffy would have been able use Leo Bazooka and King Kong Gun before his 20 minutes of Gear 4th ran out if Joker never stalled; this would have guaranteed his victory. Things didn't go that way, so i think it's fair to at the very least regard the entire fight as even.
Anyway, I'd leave it at that for now anyway.