The moshol I referred to above is as follows: (apologies for any embellishment or inaccuracy)
A man with no marketable skills begs a distant relative, a wealthy owner of many factories and businesses, for a job.
He hires him to work in one of his factories, as a kindness.
Years later, the owner, who doesn’t even remember this man, decides to visit this factory.
He calls a meeting for all employees, and asks each what his job is.
One replies that he works on the product design, another that he does maintenance of the facility, another that he does inventory, etc.
Finally, it’s his relative’s turn. The poor fellow, clearly embarrassed, sheepishly looks down and mutters, “every day I come to the factory and collect my wages”.
That’s called “nahama d’kisufa” – bread of shame.
As I recall, the Chofetz Chaim used this moshol to explain why, since Hashem created us for our own benefit, ultimately, as the Mesilas Yesharim says, “l’hisaneg al Hashem v’leihanos miziv sh’chinoso” – for the ultimate reward which awaits us in the World to Come – why couldn’t He have simply put us all in Gan Eden without all of the mitzvos (positive and negative), which are tremendous challenges?
He answers with the above moshol, and I believe it also answers why we need punishment and suffering.
Chabadshluchah, the fellow you refer to may counter that it still doesn’t explain why Hashem had to create such a system, but I think the answer to that is that a system without reward and punishment, and the benefits of earning the reward by working for it (and the possibility of punishment and suffering for sinning) is inherently not a just system.
Yes, Hashem has the ability to do anything, but that doesn’t mean it is His will to do something which is not inherently just and correct.
So, in order to create a just world with the potential for us to obtain the utmost reward and pleasure, He created a system with reward and punishment, which sometimes takes the form of suffering.
May Hashem help this poor fellow to see the truth.