I don′t understand why you don′t like it? Only because it′s too much alike TF2 spy? I believe there will be counter tactics.
Friendly Operatives, for example.
Brink is, as far as possible, quiet realistic in the possibilities you are given.
Disguise is the exception to the rule. The Security guys especially peobably all know each other.
Yeah, handing out Ammo which apparently grows on the Soldier's body. Healing/buffing/reviving with Syringes which appear to grow on a Medics body. A shining glowy paste which makes weapons go boom. Turrets which grow out of the ground. Mines which are invisible before an Operative spots them.
And the ability to change all your equipment in an instant.
BRINK is quite non-realistic in the possibilities you are given.
Disguise is no exception to the rule.
Bottom line, the game is about fun. And some people like to disguise and go behind enemy lines.