You've got your math way, way wrong. Yes, you can deduct $20,000 a year in depreciation. But that's not a tax credit. It's a tax deduction.
So let's say you are in the 30% income tax bracket. Your cabin nets, after all expenses, $100,000 per year. If you depreciate $20,000 per year on the property, your tax savings is $6000 per year, not $20,000. (30 percent of $20,000)
And as John said, depreciation is tax deferral, not a tax write off. Big difference. Every dollar you depreciate lowers your basis. When you sell, the IRS will recapture that amount.
And even assuming for a moment that you indeed had a "tax loss" of $230,000 - on this property or any other - the maximum annual loss you can claim per the IRS is $25,000, and that would be an income deduction, not a tax credit. Once your AGI reaches $100,000, that stars phasing out rather quickly.
And you can't "bonus depreciate" a percentage of your full purchase price of $640K. There's a very limited list of things you can bonus depreciate. Certainly not the dwelling and the land.
My friend, you need a new accountant.