When Zeru left the System Rider, so did the borrowed powers of Genbu leaving Jin. It immediately caused all the strain that Zeru had caused to Jin and so was the accumulated toll of the damage that his body had taken when Genbu's System Rider powers dissipated.
Jin literally fell to the ground unable to move and he too was in the same position as Number Four, spewing blood. The only difference was that the healing pain worms inside him were making it worse for him despite them healing him to the best of their abilities.
Old Flammet on the other hand was able to use the opportunity that Zeru gave to send the laser sword that was on the Mechanoid Armour and stabbed it through Gerrad. His friend tried to get out of it but Old Flammet did not give any quarters as he put the huge rifle's barrel at Gerrad's head and pressed the trigger.
Taking indefinite hiatus, rewrite chaps and post at times. tyvm