The business of originating, funding and servicing monthly-adjusting ARM loans may be the most profitable model in the mortgage market under today’s conditions, but things could get a bit tighter in the future. A new report by Moody’s Investors Service notes that narrower margins and increased competition could squeeze the profitability of the ARM lending model. But for now, the ARM model appears more profitable than either of two alternative strategies: originating and funding fixed-rate…