A>) Spios have too many abilities already. Remember they already unlock concussive grenades via veterancy too.
B>) Spios with flame nades?? Really?? Their point blank DPS is already insane, I think that this would be too much.
I mentioned earlier that the concussive grenade they have can just be replaced with a incendiary nade. I also think it's preferable to have one unit with that kind of high dps than to have a ton of scalable volks that can also run around clearing team weapons and garrisons in 1 shot