My original comment was really toward the advantage of using the same item in two or more products, based on performance, like CPUs, not all of which make the highest performance standard in each production batch. Being able to sell lower performance items, increases the overall profit. Someone from an oil company once remarked that the key to a profitable process wasn't making the product more efficiently, it was having a profitable market for the sludge.Aside from the form factor (2170), they are not the same cells. Elon has said many times the chemistry they use for Powerwalls/Powerpacks/Megapacks is very different from the auto cells, in order to allow for deeper cycles without the same level of degradation.
I admit that things aren't super clear, but for Powerwall 2s, the chemistry would appear to be lithium Nickel Manganese Cobalt
Tesla Powerwall: Cost, Features, and Complete Review
Here's our detailed Tesla Powerwall review - check out the up-to-date Powerwall costs and product specs for this popular solar battery.
news.energysage.com
Tesla Powerwall 2 Vs LG RESU Vs Sonnen ECO Vs BYD — Clean Energy Reviews
We review and compare the Tesla Powerwall 2 with the popular LG RESU lithium battery which is considered the leading competitor to the Powerwall, plus the well known German Sonnen and the large Chinese manufacturer BYD.
www.cleanenergyreviews.info
and this article makes the case for NMC and NMCA(NCA) batteries across the Tesla line up, though missing the Chinese market;
Tesla Batteries 101 — Production Capacity, Uses, Chemistry, & Future Plans - CleanTechnica
Some industry observers have in the past argued that, rather than Tesla being an electric car company, it's actually a battery technology company that happens to sell electric vehicles ... and lithium-ion energy storage systems ... and solar photovoltaic (PV) roof systems ... and ...
cleantechnica.com
Tesla shifts battery chemistry for utility-scale storage Megapack
The move to cobalt-free lithium iron phosphate batteries for the 1 GWh product could signal supply chain shifts.
www.utilitydive.com
So,... as is often the case, Elon's comment that you refer to might be kinda of true, but does not appear to accurately capture the complexity of Tesla's battery chemistries today.
BTW: 21700 is a battery size definition (21mm dia., by 70mm length) and comes in several different chemistries, identified by the suffix; LMO (21700IMR), LMN(21700-INR), and LFP(21700-IFR)
All the best,
BG