Same with 2018. Not sure about 2019, but I doubt seriously Mazda did any revisions in this regard.
I want to stress that while this is an issue for aircon "off" with outside air "on" and vent "open" conditions, this is not a major flaw in the CX-9 design. The air conditioning system as a whole works just fine and it will keep the interior cabin at a steady lower temperature relative to OAT. And, the Auto function for temperature control in the CX-9 works just fine as well. The problem is in the duct work to the outer vents inside the cabin and the way they went about sourcing ambient air entering the cabin with the vents "open" condition. The CX-9 runs a little warm under the hood and this is obvious causing the issue. However, once you close the air vents and run in the aircon "on" condition, temps will stabilize and the cabin runs very comfortably from that point forward. I've driven through OAT 102-F conditions for hours with aircon "on" and vents "closed" and maintained a spring like 73 in the cabin front and back with fan speeds at about 40%.
She's a little warmblooded under the hood and they source enough true outside air in the flow, that's all.