No, not saying that. But just feeding any old flake isn't going to cut it. Sure, they'll live... but healthy fish live longer, color up better, and resist disease more so than that of fish who do not receive a healthy, nutricious diet.
NLS is one of the best foods. There are, of course, other foods you can feed. I don't have any experience with Kens or some of the higher end Hikari foods, but there are definitely some other good options.