I think that Gabriel Reyes went deep undercover in Talon as Reaper after the original Widowmaker Incident to gather Intel on the organization that took Amile, and hopefully even rescue/unbrainwash her.
But then he found out that Talon had infiltrated Overwatch, and they planned to use Overwatch to kick-start the next Omnic crisis. He didn’t have enough time to stop them before that happened, so he did the next best thing: Gabe set it up so Talon couldn’t use Overwatch as a cover anymore.
Gabe deliberately blew his cover in Rialto instead of just snapping the bad guys neck. He knew that the bad PR from the mission would open an inquiry into Overwatch’s activities, and reveal everything that Talon was doing using Overwatch’s name.
The bad PR did what Gabriel wanted: it destroyed Overwatch, keeping it out of the bad guy’s hands for good.
Since then, he’s been hunting down the Overwatch agents that betrayed the organisation, and been working on creating his own splinter cell within Talon. Akande might think that Reaper recruited Sombra into Talon, but that’s what Reaper wants him to think. Sombra’s part of the splinter cell, and she cooks the books so Talon never figures out how many times Reaper’s mission “hits a snag” is actually him deliberately failing the mission.
Case in point: Reaper’s had several chances to shoot Winston in the face and end him. He’s never gone for the killing blow against a loyal Overwatch agent.
In the “Soldier and Ana vs reaper” comic, Reaper had a free shot at Soldier… But he shot him in his torso instead of his head, when he knew Ana was lurking in the backline with healing darts.
And when Ana revealed herself, Reaper retreated instead of taking a fight that he had no chance of losing. Talon wants Ana and Jack dead, but Reaper let them go.