It probably is a better base oil and doesn't need as much.
ZDDP doesn't care about the base oil and vice versa unless you're chasing additive response at specific temperatures. ZDDP forms in mixed and boundary lubrication where there isn't sufficient oil film present so the base oil doesn't matter.
This oil cannot contain that low of ZDDP. It wouldn't be on the shelf with an API SP starburst if it did because API mandates a minimum of 600 ppm phosphorus. All this VOA shows is that Blackstone sucks. If you were to take that same oil sample and send it to ALS, Polaris, PMS, Wearcheck, Speediagnotix, etc... you'd likely get ~20% higher values across the board.