I think when you start to lay this stuff out and playing it to its end, compound growth can not continue forever.  

it will compound astronomically!!

Albert Einstein referred to compounding as the greatest invention of the 20th century.  

How about constructing a worldwide pipeline distribution network and use compounding time to make a boat load of money?

Whether I compound the amortized $1M over 4% or 20%, that is a material amount of opportunity cost. 

If this is your first development project, you are already taking on a lot of risk just in trying something new, so why compound that with a steady interest payment coming at you each month and the potential of having to walk into a refi with a check in hand.If you are an experienced developer, that is a much different story.

In addition my 14 year old daughter has attended 2 future fortune builders classes which teaches teenagers all of those things about budgeting, compound interest,  owning a business & endless other aspects that many people go their whole lives not ever being aware of.The $50k education includes 6 members so you can combine your funds with other peoples to save money and learn the same content. 

As an alternative hypothesis I modeled my return from investing in something like an index fund, using my initial cash investment ($20k down + $5k initial rehab), adding the $6.6k mortgage every year, and compounding annually by 6%.

Not only will it take forever to break even, but these examples don't take into account the accumulation of compound earnings that you are missing out on.

The Compound effect by Darren Hardy.