This is now besides the original point, which was that in cryptography's case, "lightweight" would work like "alternative" works for "alternative medicine". Ho

This is now besides the original point, which was that in cryptography's case, "lightweight" would work like "alternative" works for "alternative medicine". However if we shift the focus to marketing, lightweight works nothing like that in that regard. They use it to imply that the product is fast, lean, to the point, contains nothing unnecessary, has fewer, but solid options, energetic, aspiring. Implying that the other products are heavier, bulkier, cumbersome, bloated, slow, overcumbered, overly complex. It's already used in for example LDAP, which I don't think anyone scoffs at (well, with regards to the lightweight qualifier), and lightweight software has its own wiki page, implying that the usage of the term wrt/ software is widespread enough to be notable. They write that this means "a computer program that is designed to have a small memory footprint, low CPU usage, overall a low usage of system resources". All this to write that lightweight conveys a good meaning indeed. About the only widespread negative usage I can think of is when people call others "lightweights", implying that they performed below expectations.