You would really have to use tools from each brand to understand.
Alot of the branding is about market share. For example, Blue Point has evolved from tools that snap on sold but, didn't make like some automotive specialty tools into a largely imported lower cost line.
Williams is an industrial brand and caters to the industrial user like machine maintenance. Hence, there's a lot of SAE sizes but, not a wide selection of metric sizes. Within williams, there are two lines, one US made, the other imported to offer a lower cost option. The imported williams tools and some blue point tools are the same aside from the name.