[Sirrotica]

The ZDDP is the cheapest additive that chemical engineers could use to fend off flat tappet wear especially during break in. There are other additives that are able to do the same thing, but they are more expensive. It's perfectly plausible to have lower ZDDP concentration and still have other additives carrying the water, instead of ZDDP, you will pay more for oils with other wear agents substituted for ZDDP.

As the engineer says in the video I referenced said, the balance of the additive package is needed to get all the additives working in the same direction. Kind of like getting all the parts in a performance engine working in orchestration. One single part won't give you optimum performance if all the parts don't compliment each other. Balancing the formula to get the most from the sum of all the agents get the best result.