This is too strong. The argument needs a way to get to the claim that Jason would benefit from knowing his supervisor was displeased, however his situation worsening otherwise is not necessary to meet this condition.

This is not necessary - the focus of the argument is if Jason would benefit from knowing, in which case Jane should tell him. Whether or not he could find out from other sources is not relevant.

It does not matter whether Jason is grateful for the information - it could benefit him even if he were ungrateful or could fail to benefit him even though he is grateful. Gratefulness is not part of the condition the argument establishes regarding if Jane should tell him.

Potential positive outcomes in which Jason doesn’t find out aren’t relevant to the argument, which is specifically trying to get to the claim that Jane should tell him and therefore he should learn.

This explains why the condition applies to the specific example. If this were not true, and Jason would not benefit by improving his supervisor’s opinion of his work, then the premises would not support the claim that Jane should inform Jason.