Re: Allvit discussion. You keep missing the biggest plus that derailleur had in terms of the market. The mechanism was absolutely unbreakable if the bike was tossed down on the right side. This is probably why Schwinn kept using them long after they'd been replaced by newer designs. And the only Japanese mechanism to match them was the Shimano Eagle with that built-in guard wrapped around the parallelogram.

Don't forget, back in the 70's the majority of 10-speed were still being sold to the under-16 set, so strength to handle abuse was of paramount importance.