I presume you have looked at used Model S/X prices recently?
2014 AP1 85Ss are still over £30k, thats roughly 40-45% residuals at 5 years old, very few ICE cars come anything close to that. Over the next few years I doubt they will fall to much below £25k, as a MG EV with far less tech/range costs more than that, and Hyundai is charging nearly £35k for a Kona, Porsche £100k for a Taycan which has less EPA rated range.
Our 75D X was cheaper to buy than a SQ7, both are now worth about the same, add in running cost savings and our X is some £20k 'cheaper' to own in real terms over 3 years and 40k versus a SQ7. Going fowards which car is going to be in more demand on the used market, a diesel SUV or an EV SUV?
Finally residuals only matter if you sell, why would you sell if the car already does everything you want, and longterm ownership costs are so cheap?
If you must have the latest and best, then yes you will be constantly changing cars, in which case lease deals are fine.
But remind me how much a lease is on a P Model 3 at present? Our fully owned X is currently costing me £40/month in home charging costs, tyres £500 every 20k, and £650/year insurance, on going finance costs is £0.
We will be keeping it at least 8 years till the battery warranty is gone, how much would leasing a car for 8 years cost?