Sir, you cannot compare an automatic shotgun with high firerate with the JG. The only valid option for a comparison is the CSG. And as you mentioned it has a spread of 0,85m which a little bit more than the half of JG's spread. So it is just natural that JG need less pellets to hit for a kill.
Let's do a weird comparison with any non-shotgun weapon. They have a spread of 0m (just a single projectile) and need 100% hit (yes I know there is only 100% or 0%) to do damage. You see where it goes? If there would be a shotgun with a spread of 3m it would probably only need 30%(just a random number below 66) of pellets to hit to do kill.
I'm not saying CSG should not be buffed, just saying it does not make any sense to compare percentages of pellets need to hit for a kill due to different spread.
Have a nice day
Edit: What I always wanted to know:
It is obvious that the JG is better than the CSG in hug range due to the higher damage and spread has barely impact at hug range. CSG becomes better with every meter more distance.
Did someone calculate at which distance the break even point is? So at which distance both shotguns perform identical and every meter more distance the CSG outperforms JG more?
Thanks in advance if somebody knows