Why can't they mediate from heaven (assuming they are the GC's mediator)? Jesus mediates from heaven over the anointed.
Also the anointed do not become angels (which are considered mortal by the WTS) but immortal spirits.
Also in the 1988 Revelation book the WTS says that the anointed in heaven would fight along with Jesus.
*** re chap. 39 p. 281 par. 11 The Warrior-King Triumphs at Armageddon ***
Others too will be involved. When sending his message to the congregation in Thyatira, Jesus promised: “To him that conquers and observes my deeds down to the end I will give authority over the nations, and he shall shepherd the people with an iron rod so that they will be broken to pieces like clay vessels, the same as I have received from my Father.” (Revelation 2:26, 27) Without a doubt, when the time comes, those of Christ’s brothers already in heaven will have a part in shepherding people and nations with that iron rod.
*** re chap. 10 pp. 52-53 par. 18 Abhorring the “Deep Things of Satan” ***
To those Christians in Thyatira, Jesus now speaks heartwarming words. They also encourage anointed Christians today: “And to him that conquers and observes my deeds down to the end I will give authority over the nations, and he shall shepherd the people with an iron rod so that they will be broken to pieces like clay vessels, the same as I have received from my Father.” (Revelation 2:26, 27) Indeed a wonderful privilege! This authority that anointed conquerors receive at their resurrection is a sharing with Jesus in wielding the “iron rod” of destruction against the rebellious nations at Armageddon. At best, the nuclear firepower of those nations will sputter like a wet firecracker when Christ dashes his enemies to pieces as he would vessels of clay.—Psalm 2:8, 9; Revelation 16:14, 16; 19:11-13, 15.