Great Paul. I learned more from Engineers in my life than from Accountants. It's a thing called "logics and analytical thinking".
Accountants are focused on balancing. Engineers focusing on twisting it around until it works.
Let me try it another way around.
Let's assume that you have a wife and for tax purposes, you file a joint tax return. But from a financial and legal point of view, you keep your personal finances strictly separate from each other. You own the primary residence, she owns the rental properties. Your interest expenses have increased but you will not claim the additional interest on your Schedule A for reasons we discussed.
You have $ 200 K in your pocket. Your wife, the owner of rental properties proposes to you lend her money.
Now you are the Bank. You are lending her money as a loan, and she pays interest to you. Comes tax time, you have to report a taxable interest income on your 1040. She, in turn, repays the mortgages on her rentals and claims the interest expenses she pays to you as tax-deductible interests on Schedule D. (her rentals)
Comes tax time, you consolidate your financial positions with hers. You have to report your interest income on Schedule B and she will claim her interest paid on Schedules D (her rental properties) Since you file MFJ you are back at square one. Yes, interest paid for investments is tax deductible but the one who receives the interest has a taxable income.