How do you feel about 10.5” barrel ARs for home defense?

I bought my first gun about 6 months ago. I bought a PSA 10.5” upper and a prebuilt pistol lower before the last election because of riots. Since then I have bought a hand stop, QD sling, Flip up sights and 12 standard capacity mags. My question spurs from a convo from an older clerk at the gun shop. He looked at me super funny when i told him I was using it to protect my home. He suggested a handgun in 9mm because of wall pass through. I thought about this and figure i live in a brick house and found a place of no return that would be safest for the neighbors in a defense situation. I also keep two mags loaded with 55grain predator rounds to cut down on bullets going through walls. Would you use a short AR to protect your home? What should my next purchase be (I plan to purchase a red dot- budget suggestions welcome). I plan to buy a G19 when these next two stimmy checks are received. Did I make a mistake? Edit: added details about setup via /r/CCW https://ift.tt/3leGUFy