Neither is wrong but depends on your objectives. 

I know in the beginning of a loan you can just write off the interest because that’s all your getting charged but later down the road you pay more down on principle so couldn’t an investor lose money overall say if the principle is over the amount they can depreciate since investors typically use depreciation to offset the principle cost?

The irony of blindly pursing objectivity in a very subjective process is lost on the ones I've met.

I've doing all my calculations as if my loan interest is tax deductable and even though the principle is not I can claim depreciation to reduce my taxes.

Plan to utilize new urbanist and smart growth principles for planning and design.

We purchased and paid off our home in 5 years using the Principles of Dave Ramsey. 

@Rob Ferdinand since you have to make the full mortgage payment inclusive of principle I include it in full into cash flow models bc the key is to ensure the property is self sustaining with the debt you need.

Made my profit objective.

So there still exists a market, however as mentioned above pricing is still far higher than it was years past, making it more difficult to meet return objectives. 

You can solve for the principle and interest payments from there, which will lead you to what a loan balance can be.