Earlier quoted context omitted.
True, but we can't be sure that no breakthrough in fuel cells or supercapacitors will make batteries obsolete.
We can't be sure that there won't be a breakthrough that will make all our phones and cars run on adenosine triphosphate, like everything else on this planet. But right now we have to work with what we have, and whatever knowledge and experience we thus gain will likely be useful post-unexpected-breakthroughs anyway.
And at 507.18g/mol + 18g/mol for the water, that's only about 87J/g, which is worse than lithium ion batteries.