Well, there was a lot going on in the late eighties and early nineties with the development of OS tubing so I'm pretty sure there's some substance to Schwinn's claims probably mixed with a little marketing hype.

The 1995 introduction of Reynolds 853 ("the world’s first commercial air-hardening steel for bicycle frame tubes" according to the Reynolds timeline) made TIG welding of thin walled OS tubing practical because the heat from welding actually makes the welded joint stronger in air-hardening steels. But the Tange OS tubing Schwinn used for the TIG-welded PDG Series Paramounts in 1989 and 1990 and jointly developed by Schwinn and Tange was not air-hardening, so was probably designed with thicker butts in the heat affected zone (HAZ) to mitigate warpage from the welding heat.

The heat treated True Temper OS tubing first used in Waterford Paramounts in 1989 was also jointly developed by Schwinn and True Temper and wasn't air-hardening either. Because it was heat treated, overheating during brazing could weaken the tensile strength of the tubing, so in addition to using low temperature silver brazing I'd have to guess the tube butts were appropriately thicker walled to resist warpage and strengthen the tubes at the high stressed joints. I'm not sure what part the development of custom short point lugs played.