MMMMM.... the issues with flat tappet cams showed up in the 2005-2006 timeframe, < a year after the mandate to lower the phosphorous levels in the lighter motor oils. So the conclusion about the importance of ZDDP is pretty clear. The question come up more about how much do you need and at what spring pressures (which drive lifter to lobe pressures). And yes, excess ZDDP can cause documented issues, but being at the 800 ppm level for a flat tappet cam and heavy springs is inviting lobe destruction. The prior limits were around 1200 ppm and flat tappet cams lived well on that.
