I've read this three times now and can't figure out what you're saying.
Kobold has it right. It just encourages casters to go nova and rest quickly, since they will burn through spell slots quicker if their options become cast a spell or do nothing of value.I think that they're saying that it will exacerbate the 15 minute work day rather than solving it.
Out of all the reasons that spellcasters are problematic in 5e, their cantrip damage is rarely an issue.