I don't have the citation for it, but I saw a tweet from Mike Mearls that addresses this, Cantrips are intended to use your character levelCantrips are intended to use your character level. The example give I believe was a lvl 20 high elf barbarian being able to cast firebolt at max level. The spells refer generally to character level and not spell caster level.
The Sage Advice Compendium confirmed this when it was published.