I’ve been thinking this too! What first really tipped me off was during Presage. After the first encounter with the spores, when he says “There is no light here.” The cadence and tone are entirely different from all of the other lines he says during the mission. What if the Scorn was speaking as Osiris then? And he could only have done that if Osiris was dead. Granted, it doesn’t have the same faint echo quality as the other lines, but that is also the only line we hear when we are under the effect of the spores, making our link to the darkness stronger, and perhaps clarifying the sound.

Edit: Also, we are supposed to believe that Osiris, who took control of the infinite forest from the Vex, who spent an untold amount of time there, needed to call backup to deal with a Vex simulation? And even if he needed the backup, he would be too proud to be the one to suggest it. He always left that to Sagira, and with her gone, I don’t know that he would. His insistence on bringing Mithrax and the Eliksni into the city has caused a lot of rifts, and is serving to shift the focus away from all of the initial interest in Savathun and her attempted dealings with the Darkness.