back in the early years, the steel alloy tubing available for lightweights (Reynolds 531, Columbus, Vitus, Falck, etc.) was not appropriate for high heat joining (such as any form of welding involves, Tig or otherwise) because it caused the over-heated areas to become brittle and prone to break. Lower heat methods such as brazing with bronze or silver alloys was demanded...many frames were joined without lugs but still using brazing techniques: fillet-brazed AKA "bronze welded" in the UK. Then modern metallurgy stepped up and provided steel formulations that could withstand (and even benefit from) the higher heat of welding...that's where we're at today, and these tubesets can be just as light as the old stand-bys, even lighter in some cases, and you can even use lugs and braze them if you wish.