Are we talking about proper 'leases' on propane tanks (usually very large propane tanks, meant to be attached to the side of a house/business)? Or are you referring to the usual 20 lb tanks that are stored underneath grills? Because everyone I know 'owns' 20 lb tanks. Nobody pays some monthly fee to lease them. You just typically exchange the entire tank, fuel and all, for whatever other tank someone has.
If that was how the battery swaps work, then I'd agree, but that isn't what Nio is doing. You are paying a monthly fee for the battery in addition to paying for each swap.
By your own air quoting you know they don't own them.
The gas companies own those tanks and responsible for inspecting them whenever they rotate back for a refill.
The also choose the economic deal, they've baked a "lease fee" into their costings and are happy enough to ignore tanks that are never returned as most are returned, the total volume is high and the costs of chasing strays (that have an expiry date in any case) are greater than the value of gathering them back.
It's possible that EV batteries will one day have the same deal as propane tanks, more or less wrt to an explicit lease fee Vs an invisible one.
There’s no ambiguity here. You own the 20 lb tanks. Now, after they expire most propane companies won’t refill them, but otherwise it’s yours to keep. You could argue that this isn’t actually “owning” it, but for all intents and purposes it is. You’re responsible for making sure it’s not expired when using it, although the companies that do all the exchanges are responsible for making sure tanks they sell are not expired.
If that was how the battery swaps work, then I'd agree, but that isn't what Nio is doing. You are paying a monthly fee for the battery in addition to paying for each swap.