The powers are not predicated on which power pill is used, or the decisions of a third party. The pill awakens powers within a person subjective to that person. No matter which pill an individual person takes, that individual person will exhibit the same power each time. The power pills is more like an evolution accelerator for that individuals specific DNA.
An example of this is the Jamie Fox character’s reluctance to use the pills. He knew what effect it had on him. He was only willing to use it when his allies were safely isolated in the lifeboat. The female scientist character also knew the effect a pill would have on him. That is why she panicked when she saw he had one. Also, the mercenary guarding Jamie Fox’s character might not have known his exact power. But, he had probably heard rumors of its last use.
Other examples of the powers of an individual being the same for each use is the fact that the powered soldiers were so adept at their powers use. They knew what the powers were and how to best utilize them from experience. Something Joseph Gordon Levitt’s character may not have had his first use shown on film. The same goes for the chameleon bank robber and the fire demon drug dealer. In the case of the drug dealer, his face showed evidence of previous burns.
Something that argues against the opinion that powers could be altered, chosen, or objective is the disadvantages of that very scenario. From a tactical point of view, having an unpredictable power would be a very limiting factor for a character. For instance, not being bullet-proof when you are expecting and counting on it in Joseph Gordon Lovett’s case at the docks. And, having an unknown power during a high stress, high stakes moment like combat would be an added distraction and problem for the user. An example of this is General Zod’s soldiers in Superman.
One thought that does cross my mind is whether the power exhibited by an individual is dictated by their physical makeup, or their mental or personality makeup. Could a person’s prior experience or environment influence it? For instance, Jamie Fox’s character was an Army Ranger. His powers were very offensive and combat oriented. Jospeh Gordon Levitt’s character was a cop. His powers were very defensive and meant to protect. The tall, lanky mercenary was almost elastic. The bank robber, whose profession was subterfuge, was a chameleon. Something latent in their genes or personality could have pushed them into those professions. The power pills simply amplified it.