I strongly believe the temperature management will help pack longevity in any climate. After nearly two years with my FFE, I have noticed no degradation in range.
A battery thermal management system can't improve pack longevity if it never turns on. What temperature does the FFE TMS turn on at, on the high side? Yes, I've seen the message of "It's hot, please plug me in" for FFE on warmer days, but I don't know the actual temperature range of the FFE TMS.
My typical battery temperature in the summer is in the 60F to 70F range. I've never seen a battery temperature above about 85F in my Leaf.
What battery temperature does the FFE TMS turn on to cool at? And what temperature does it cool to? If the TMS never cools the pack, how would it improve pack longevity?
Actually, it is worse than that. The Leaf battery is cooled by airflow, the FFE has more insulation around the battery pack and is more cooled by the TMS. Charging and driving will both increase the temperature of the FFE battery pack in an isolated box until the TMS turn on. So the average temperature of the TMS system is likely to be higher than the airflow cooled battery, at least in cool climate places.
In warmer places, of course the TMS will improve battery life at the cost of higher energy usage. In cool places, no improvement, and might even make it very slightly worse.
Battery life model on the Leaf Wiki suggests well over a 10 year life in my climate. I'm ok with that. I can see why someone in AZ or hot areas of CA might not be as happy with the Leaf, and would rather have an FFE.