The oddity is that trailers are for the most part only available in less than 3500, 3500 and 7000 lb increments due to axle ratings. That means that it is not worth even towing a standard medium duty 3500lb rated trailer such as a Uhaul 5x8.
As passengers, unloaded trailer weight and anything in the vehicle need to be included in the tow capacity rating, adding a 200lb driver plus 350lbs of passengers (one big ass wife or a slimmer hipped model with a couple of school age kids) plus 100lbs of luggage and a 1000lb empty weight trailer (unloaded 5x8 Uhaul utility for example) leaves you with less than one ton of trailer cargo (200+350+100+1000=1650 subtracted from 3500=1850lbs net towed capacity. Not much at all and almost not even worth towing a 5x8 utility trailer. That puts you down into the small Uhaul or even Harbor Freight fold up type trailers that can be pulled by a compact SUV with a 4 cylinder engine. Puny.
I just don't believe the CX9 is that wimpy even without a more robust transmission cooler. The Aussie CX9 is rated higher than the US model presumably just because of different hitch and I recall the version down under is rated to tow somewhere around 4000-4500lbs. If so then it is not a transmission issue at all but just a marketing decision (bad one) to not offer a Class 3 hitch and 5000lb rating. I smell a zoom zoom marketing call rather than a carefully calculated engineering decision on this.
