There are those who say Expert is too hard and is impossible, and there are those who say the opposite, that it's absurdly easy and can't be relied on for a challenge. I say it depends on circumstances outside of just difficulty, but who am I to say anything? I'm just a dude who beats Expert Aztecs on black sea then gets wrecked by Hard French on great planes.
How about a compromise.
Is it possible to add extra difficulty settings?
For example, keep the vanilla Sandbox-Expert, then add in Difficulty 1 through Difficulty 9, with 1 being a computer that literally suicides its vills and does nothing, and Difficulty 9 being a Skynet AI with 10,000x better production and auto-spawning tommynator trucks out the TC.