I understand what you trying to say, but US issue with high sulfur gas has nothing to do with intent of ACEA C3 oils. In 2004 they were introduced for vehicles with DPF, but in 2009 EU moved to ULSG, which allowed manufacturers to switch from A3 to C3.
My point is, that that engine you had is actually designed from beginning for heavy oils (as all Euro engines are, even today). So, if that particular engine in your car had issue with heavy oils, issue was somewhere else, not with oil. If catalytic converter behaved differently, why? What happened? Oil was made out of ZDDP alone so it clogged immediately? IMO, nothing to do with oil, but engine was lemon. Light oil was just hiding real issues more successfully.