There is a Sefer called רש״י כפשוטו (it’s a Chumash with rashi and an explanation on rashi) that brings a Gemara in bava basra that says it doesn’t say מיתה by דוד המלך because his son Shlomo followed in his footsteps and the same could be said here
Coffee,
1. It is not Rashi’s derech in his pirush in chumash to be understood based on an obscure Gemara. He writes his pirush assuming a child will read it and understand it at face value.
2. Even if you want to say that this is Rashi’s intention in his pirush on Vayechi, it is bipashtus not able to be his intention in his pirush on Taanis where he adds the part of נדמה להם etc.
The main discussion in this thread is regarding Rashi’s pirush in Taanis.
[And, as I have demonstrated in an earlier post, Rashi’s pirush on chumash need not match his pirush in Shas.]