After analyzing the system, the Collector came to understand that it had already chosen its form and made certain modifications such as replacing the hobgoblin thrall's core with the Jotnar core.
These modifications were made sub-consciously by the Collector whilst it was engaged in the White Voice's psionic space, likely with some assistance with the additional brain it now grew within the pit of its stomach.
The Collector was certain of this, even if the engagement with the psionic space of the 'White Voice' had muddled its memory banks, for all the shifts it had conducted to its body were those that it would have made itself.
Its physical form, too, was that which the Collector would have likely ordered consciously.
Expect some action soon with the Collector really showing how much insanely stronger it's gotten. I would say that the Collector is now at the stage where it is in the higher end of power in this world, but not fully at the highest.