Blue
Ravenous Bugblatter Beast of Traal
Literally, unless your fewer encounters last longer then 6-8 normal encounters, it does not begin to do what you are saying it does. "Helps deplete resources", as discussed, is insufficient. "Have completely depleted resources every day and forced 5-10 rounds of cantrips" by the end of the day is the balance point. You use up every single slot from your casters - the casters have still be doing more the the at-wills during every action. You need to take them past that point. That's the class resource recovery balance point they built into 5e.Well, first, I'm not talking about "a single round of combat." A deadlier combat would likely have multiple foes, or at least one foe with lots of actions, legendary and lair actions, and all that sort of stuff, and monsters moving around instead of going toe-to-toe, causing it to last long enough that the casters will have to use both higher-level slots and cantrips. Also, if you have both combat and non-combat encounters (obstacles, hazardous conditions, social encounters, etc.) then that also helps to deplete resources.
And again, since the fewer longer combats do make those long lasting spells even more powerful, it's even more cantrip time to balance out than in 6-8 encounters/day.