No, it's not. Energy density is only relevant for today's uses of batteries - car's, laptop and the like. If energy density was all that mattered pumped storage would be utterly useless as it energy density is abysmal. The reality is pumped storage is 80% efficient, and is good for 10's of thousands of cycles (basically unto the dam silts up), and base storage medium (water) is dirt cheap. As a consequence we store and discharge gigawatt hours of energy using pumped storage every day, which I suspect more than all those batteries with higher energy density combined.
If you want another comparison, there are more vehicles using lead acid batteries than there are using lithium - yet lead acid has a horrible energy density. (You are thinking this is wrong - but you are thinking cars. There are far more golf buggies and indoor forklifts and the like out there than there are cars.)
They say the voltage of this battery is around 1/2 that of lithium - which I suspect means much than half the density. But Aluminium is cheap, more common and lighter than lead, and they are talking 10's of thousands of cycles. If this works it will change the world - regardless of it's energy density.
(I guess phys.org is just reprinting the Stanford press release)