it's not holding off the attack from after you build the tc, it's taking down the tc in the first place.
1) as you said you attack at 7 minutes, only isis and ra wouldn't have an army by then, and as you said it wouldn't work against them because of their towers. By 7 mins norse would have 20 hesirs/rc/ulfs, attys would have 20 turmas, greeks other than hades will still have 10 or so soldiers atleast. Not to mention the free myth unit at the start of classical.
2) if this happened to me and i didn't have an army for some reason at 7 mins, i'd micro my tc fire so i take out all of the villagers, then how would you build the tc without villies.
3)if you fail to take out the tc, you're screwed for the rest of the game.
The ra villager rush works because of the resistant villies with greater attack, and the shifting sands gp to get them there earlier. Ra villie rush gets 20+ villies at the tc at 6 mins, with the pharoah taking out the free myth and then empowering the tc to get built quicker.
The whole point is being able to take down the tc, hades will struggle to do that against decent players.
Accept No Immitations
-Wildturkey