20% lost at 400 cycles. This isn't so bad if it really offers 4x the capacity. In terms of usage it will last 1600 cycles comparatively speaking. Which is still far better than Li-Ion.
"In 2003 it was reported the typical range of capacity loss in lithium-ion batteries after 500 charging and discharging cycles varied from 12.4% to 24.1%, giving an average capacity loss per cycle range of 0.025–0.048% per cycle."
(https://en.wikipedia.org/wiki/Capacity_loss)
And that was twenty years ago, things probably have improved. I think you have a wrong impression what is meant with "a battery lasts X cycles". That does not mean that it will be at zero capacity after 'X' cycles, but usually that it is down to ~70% of the initial capacity.
EDIT: Sorry, I missed the "comparatively speaking", so you mean when including the 4x capacity. You are right, of course.
Something that baffles me is how hard it's become to replace the battery. I had the original generation Galaxy S -- I loved that thing, because there was a little latch mechanism on the back-side. With a firm tug, the rear cover popped right off, allowing you to pop the battery out. It took less than 10 seconds to do a battery swap, which I used to great advantage while traveling (carried a second battery with me). Of course, back in those days, the typical battery capacity was not nearly as good.
In any event, I wish I could still do that with my current phone. It would be super slick if there was a tiny auxillary battery or 60-second hold-up capacitor too, so you wouldn't even have to shut the phone off.
Why is this baffling? It makes perfect sense for batteries to be non-replaceable: you can make the phone slightly thinner, and you can charge owners a small fortune to replace them, which will usually result in them simply throwing the device away after a while and buying a new one. Just look at Apple: they pushed non-replaceable batteries (and also removed headphone jacks in favor of expensive airPods), and people love iPhones and can't wait to get the next version, even if it costs $1399 and they have to sell their kidney to buy it.
So its not even close yet
Yes, if you compare just capacity fade, that's true. But the longevity of LiFePo4 comes with a lower charge density than Li-Ion, about 170 mAh/g. This NaS battery currently has 1017 mAh/g, so almost a factor of 6. If the capacity is higher, you don't have to cycle as often, but of course, mileage depends on the use case.
The higher capacity NMC batteries are constrained on nickel production.
If the 5999th charge is only holding appropriately 60% of a LifePo4 battery you don’t get 6,000 cycles * full battery capacity.
It would be very nice if batteries were super predictable as in 'perfect until the 6 thousandth cycle and then dead', instead you get this gradual drop-off to the point where a battery is no longer usable for its intended purpose. Whether or not that is at 60% of the original capacity or not is moot if it doesn't make it to the 60% in the first place (lots of batteries get murdered well before the end of their design life), on the other hand if that means that the drop-off itself slows down then you might be able to get much more life out of them when treated carefully.
The big ones - in my experience, which is obviously not the final word on this - is to ensure that you don't charge batteries when they're very cold, that you don't use currents in excess of what they're made for (and preferably a bit below that) and that you don't subject them to mechanical stress. If you live by those rules you can make them stretch for a very long time, enough for technology itself, rather than that battery, to make your battery obsolete.
Witness the old lead-acid batteries used in cars, telephone switch boards and submarines. In cars they would last a couple of years at best, in telephone switch boards and submarines they would routinely outlast the rest of the installation.