However, I would really like it if a lender could use my brokerage account as my “skin-in-the-game”, vs putting 10-30% down on the deal in cash.

Then you will have some skin in the game to purchase your next rental property etc!!

I know there's a million ways to skin a cat and it comes down to personal preference, but my CPA seems so adamant about not paying my house off that it has me second guessing doing so.

The point of a fan or window in a bathroom is to get moisture and bad smells out. 

And also they want u to have more skin in the game since it’s not your personal residence.

Obviously banks require you to have some skin in the game but ideally maximum returns will be achieved with as close to 100% financing as possible.A income property that can not produce positive cash flow with 100% financing will always require that the investor buy their cash flow with their own money.

No skin in the game.

If they have skin in the game, like you do, then you can feel comfortable.  

However if you have tough skin and can handle C- to D tenants and neighborhoods you can definitely make a killing if you buy right.

Also have you considered partnering with someone who is already experienced and has skin in the game?