I hope you are 100% correct. Maybe you will be. But we don't get to run a hundred trials and use the average, we get one shot at this.
Other countries have had rosy prognostications in years gone by, but the market didn't live up to their plans. There's no disputing that you are using the most prosperous years of the most prosperous country the world has known as your baseline, and assuming things will be about the same going forward. Trees do no grow to the sky. If you look at the demographic, economic, cultural, and political changes in the US since 1950, it's very hard to argue persuasively that the situation here hasn't changed in very important ways.
All of this is a good reason to take a "% of year end balance" rather than an ongoing inflation adjusted dollar amount. Whoever is right about future growth rates, adjusting as we go will let us enjoy it a lot more if things go through the roof, or successfully pare back if they don't. That decision (% of year-end balance or straight inflation adjusted dollar amount) probably makes a LOT more difference than whether we take 2.5% or 4%.