Dual pack certainly offers a substantial increase to magazine depth, it is just unfortunate that so much of the VLS space would be wasted in a dual-pack configuration relative to a tri-pack configuration.
On the other hand, it nicely complements HQ-9B - not as supplement, but actual high altitude complement. It's still a full on MSE missile.
Cut a bit more - and you're with PAC-3/9M96/HQ-16C class weapon, which is a performance choice between lower(HQ-16C/9M96*) and higher(PAC-3) altitude performance.
HQ-9C does not look like a choice, it can do both equally, yet imrpove ammo depth at most useful engagement distances.
*i mean yea, 9m96 keeps both thrusters and aerodynamic surfaces - which sort of does both...but this way you still get drag/weight/volume of two solutions, while having less thrusters. HQ-9C will likely both fly way further and be a much better ABM with better performance and footprint..