Adding more party members doesn't decrease difficulty linearly.
Don't split exp linearly then?
But jokes aside, it's NOT that important, in case you missed it.
People already openly stated that they would be willing to "take the hit" to the overall balance as long as they can have it as an optional feature.
What we are discussing here are just "quick and dirty" fixes that can *mitigate* the issue, not achieve the perfect solution.
There's a saying among DMs: "If encounters are too easy, just add more goblins."
Or give one extra "level" to one or two humanoid enemies or whatever else can apply, frankly.
The concerns about "keeping the perfect balance" are a bit of a joke in a game that is not exactly perfectly balanced to begin with.
