The designs for Rainbow Six Siege operators don’t spring up fully formed. They come as a result of a lengthy iterating process where ideas are prototyped, playtested, and refined. The original design for Capitao cast him as a healer – and while those early designs didn’t work for his role, they eventually became the basis for Finka.
Rather than his current crossbow configuration, which launches bolts with a variety of offensive effects, Capitao would fire darts at teammates to heal them – sort of like Ana from Overwatch. The issue was that line of sight between teammates is often difficult to maintain on the attacker’s side, as players scatter to flank and outmanoeuvre the defenders.
So then the developers thought about a healing attacker in a different way – what if you got healing as a global effect, which you could trigger to affect everyone on the map? So Capitao ended up in his current form, while Finka picked up the healing abilities the team had settled on. The rest, as the saying goes, is history.