Without knowing what wire they used to wind the pickups, it's not really possible to make a direct comparison between the kit and real MM pickups. If they used thinner wire in the kit pups, that would account for a fair bit of extra DCR. Also, unless you know what strength magnets they use in kit and MM pups, it's hard to gauge which has the higher output. Wiring the stock pickup in parallel will also knock 3-4dB off the output compared to series wiring.

Most active EQ systems are designed to work with standard passive pickups - only the dedicated low-Z pre-amps like EMGs have are really designed for active pickup usage. I believe the Belcat has a small 3dB boost with flat EQ, but that's mainly to accommodate for the 3db drop in volume with both pickups connected to the blend pot in the mid-position if used as designed.