2 Iyar (Acharei Mos-Kedoshim)

Rashi on Vayikra 19,3 says that Kibbud av v'aim is written together with Shabbos to teach us that honoring parents isn't doche shabbos and its the same with everything else. Typically the way of the Torah is to teach us the biggest Chiddush and I know for sure the smaller chiddush. If so, why does the torah write it with Shabbos to teach us everything, it should have written Kibbud av v'aim with a regular lav that only gets malkos as a punishment and I'd know for sure everything else. Why write it with such a chamor lav like shabbos to teach us everything?