My opinion only, and this is what I do with my variety of vehicles. My research has been if your transmission is in good shape, refreshing your fluid will improve the physical properties of your fluid, ie closer to new specs. If your transmission has worn, changing the fluid may result in slipping because the wear products in the fluid is actually helping move the car. With clean fluid it will slip. If we agree on that, how does lifetime fluid impact this thought process? There will be a point that that fluid has partially broken down. Just like he said in the video, nothing lasts forever. So eventually the fluid will have degraded and start doing damage. And if you refresh, it will be further from being the cause of failure. Doesn't mean something else won't go wrong! 😞 Looking at what came out of my transmission, I will probably repeat the drain and fill next winter. The fluid had same consistency as new, but definitely was quite dark, compared to the clear green new. Hey, new fluid will not hurt if your within "Lifetime "!
I've been hearing more and more about the notion of once you reach a certain mileage (i.e. 150k or something), it doesn't really pay to completely drain and flush the transmission fluid for the reasons you stated. It was, however, stated that you can always add more fluid if it's reading low, which has the benefit of keeping the necessary amount of fluid in the transmission, while still maintaining those other physical properties.
I'm personally a little suspect of that, though it's obvious over time that the metals do wear and tear, and thus collected into the fluid itself. The other aspect of this is does that include transmissions where the filter cannot be easily changed like ours? The KL's transmission requires a complete removal of the unit itself, and taken apart do replace the filter. It is physically inside the casing.
In most conventional transmissions though, replacing the fluids and filter is typically an easy job, but not so in a vehicle like ours. Maybe by flushing the fluid out instead of just filling it back up, you're prolonging the life of the transmission since what is absorbed into the filter doesn't really re-enter into the fluid to circulate anyway, but the filter will continue to get more and more built up with wear metals, and other gunk that might accumulate.
Perhaps someone else with some more insight can chime in though.
EDIT: And there's the elephant in the room too. How long is "lifetime" when it comes to fluid, and from a legal perspective, could it be argued if my transmission were to blow up tomorrow, that falls under Stellantis' problem rather than mine because I, the consumer, believed a lifetime fluid meant it would last hundreds and hundreds of thousands of miles? The next question though is does lifetime constitute how old the car is, or how many miles are on it?
Interestingly, the 9-Speed in the KL, while a Chrysler-spec unit, is still a version of ZF's own 9HP transmission. And if you look at the maintenance intervals of vehicles with those exact transmissions, it certainly is not listed as "lifetime" fluids. Take the 2020 or newer Honda Ridgeline (and other Honda models) that use the ZF 9HP. There are maintenance schedules for the transmission, and do not say lifetime fluid, at least I didn't see it listed. My 2014 Owner's Manual for the Cherokee KL even states,
"Under normal operating conditions, the fluid installed at the factory will provide satisfactory lubrication for the life of the vehicle.
Routine fluid and filter changes are not required. However, change the fluid and filter if the fluid becomes contaminated (with water, etc.), or if the transmission is disassembled for any reason."