The corpse possession thing was a power limiter as with scathach, which I’m fairly sure was why xande wanted to open a big voidgate to let in cod of darkness instead of making a vessel. Please tell me if I’m mistaken there, I can’t check. Voidsent generally seem to obey the more souls=more better, zero’s cowardly voidsent buddies and diabolos/diabolos hollow being some pretty non-controversial examples. Voidsent are weird though, so it probably depends primarily on the manner in which they were summoned. Allag’s voidgates and mhach’s pre-calamity area of expertise are largely inaccessible in the current setting with the caveat that the player encounters them fully functional etc. there’s also the voidsent of eureka who may be an exception to the summoning thing seeing as the whole isle took a dip in the aetherial sea instead of inviting them in directly.