Yeah, the basic premise is silly, if he is that weak then rather than becoming an adventurer he should just become a potion seller, he already proved his potion is better than most generally produced ones, I'm sure there are many high ranked party that would be willing to buy it.
With that 'I hope Tommy would send some money to my family' comment, I would assume he became an adventurer not because he particularly wanted too butt because he wanted to give money to his family, in which case, him being a potion seller would be more profitable and safer than going into the dungeon and getting whatever money you got there split up with many people. I bet his share is smaller than others too.