Battery tech will evolve, but also look at how much it has changed in the last 10 years...
went from nimh to lithium... pretty much that is it, larger battery packs and lower cost... nothing stupendous has really happened, just incremental improvement.
I leased my 2 Fiat 500e's because they were "compliance cars" and I figured Fiat would not keep them as a product long term (which has happened, they are no longer made)... they had short range, so you worked the battery hard, and the replacement battery cost was ridiculous.
With the warranty on this car and the battery and the longer range, and the uptake of the Niro model overall, I felt it was not a large gamble to buy (i.e. something fantastically better comes along in a couple of years).
My experience with buying cars since 1969 has been buy something of reasonable quality, maintain it well, pay off the loan and it will last you over 100k miles. So far that has worked well, and I have spent way less than leasing, because I have the car for a number of years with no monthly payments, and the yearly repairs are usually 2 to 3 monthly payment equivalent.
Greg