There are two ways lugs are made. Some are stamped from sheet steel and other are investment cast. Stamped lugs are have been around forever and there is nothing wrong with them. Almost all older bike were made with stamped lugs. Investment cast lugs have a somewhat shorter history and are more expensive and are sometimes more "elegant", for what that's worth.

You like the bike? Go for what ever upgrades you want. There is nothing wrong with the frame's construction.