Great question - these roles correspond to our notion of engineering archetypes (https://triplebyte.com/archetypes), which define what concentration of skills a company is looking for for a particular role. In this case, full-stack indicates a web focus, while a generalist engineer is a more, well, general programming role - often one that requires less specific web knowledge.
You list six broad categories on the archetypes page, but only five made it onto the salary page. The "Low-Level Systems Engineer" got lost. That is the only one I care about. That's me, all three sub-categories, and also what I posted about today on the "Who Is Hiring?" article.