I feel like these two points have been overlooked in regards to balance.
Due to how slowly gems are generated two players who have bought different red gem upgrades but have otherwise identical set ups will have vastly different progression and will take a long time to catch up, if they ever do.
Then you add the random factor, and all of these make an impact on your speed. Card set ups completely change progression for an entire prestige; which treasures and how many will obviously changes progression again; what you're able to buy from the merchant/bank is random; the entire Halloween event was random; presumably the entire Christmas event will be random. Even progression in the mines (pickaxes), horde (heirlooms) and farm (gold/rare drops) are random.
There are too many variables to be able to balance around a hypothetical "typical" player.