If you were buying stock or putting it in a 401K, it's not an expense. You can easily use that for income.
If you bought a car or furniture with the money, that would be an expense. A capital expense since you'll still own the asset, but an expense, right?
A house used as your personal residence falls somewhere in between. It appreciates, but you still don't get any income out of it, unless your retirement plan includes eventually selling it. So I consider it a lot more like a car or furniture. I have something to show for it, but it doesn't give me any money. If my back is against the wall, I can downsize or sell it and rent, but that's not my plan.
That's why I consider it a capital expense, and I wouldn't say I could spend more money on other things because of this.
If you tried this through firecalc, how would you account for the cash outflow with the mortgage payment?