D&D's Terrible CR vs Overly Balanced Encounters
If D&D's CR is notorious for being bad and having nothing but perfectly balanced encounters is long term boring, why not just stick to CR religiously and let the two problems cancel each other out?
Balanced encounters doesn't mean every encounter is just as difficult, it means the GM knows how difficult the encounter is going to be. Any system with good encounter building has recommendations for the level of challenge.