With battery leasing you’ve got a shell of a car you presumably pay for, and lease the battery. Leasing the entire car and also being able to do battery swaps is an advantage, but if you own the car then now the company that does the battery swaps dictates how good of a battery you get in a swap. Again, not sure a lot of people (myself included) would be on board with that.
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.
Kleenheat and other gas tank providers are responsible for tank inspectections and rotating out tanks that are getting old and unreliable.
Hot battery swap in Taiwain is logged up the whazoo for seamless ePurchase; you swap a battery for your vehicle and use it - time of purchase is logged, vehicle mileage is on your app, if a battery fails to deliver the expected milage | charge then there's no real issue, data is available and it's easy for the provider to fail that battery and provide customer with replacement and redress an economic issues.