Stoutstien
lunk
Sacred flame explicitly bypasses cover where other spell as you say rely on LOS from the origin of the spell which in turn rely on the LOS from the caster.Cover provides bonus to Dex saves, yes, but cover for spells is determined based on line of “sight” from their point of origin, not from the caster’s space. This is relevant for spells like Sacred Flame, for example, which is avoided with a Dex save, but the point of origin is in the target’s space, so there is no way to gain cover from it.
There isn't an attack cantrip I can name that doesn't follow this. You still need to 'see' the space for chilling touch hence cover.