Shinra burns down towns if they need to, but that doesn't mean it's always their first choice. If something isn't important enough, they'll let it go.
Honestly, I thought Dirge made more sense than AC or BC (maybe not CC). The in story explanation for why it was created was that President Shinra wanted a trump card if SOLDIER ever betrayed him (and he was right to worry, as it turns out). However, the entire project was a fuckup...Nero was too powerful to control, Rosso was too bloodthirsty, Shelke needs regular mako baths. But once the project was begun, Shinra had to keep feeding it, because you can't easily exterminate a couple of thousand soldiers without resistance.
As to why they were never used, Shinra knew they would kill anything in their path, even their allies and have to be wiped out, and then the whole project would come out and the public would be pissed off about all the kidnappings. I mean, Rosso apparently kills a thousand of her own men for no reason after they escape.
Sephiroth's powerful, but he dsn't know the army will follow him. And why risk death at the hands of Shinra for something he doesn't even want? He doesn't particularly want to rule the world until he thinks JENOVA deserves to.
I don't remember where it was explicietly said that in case SOLDIER betrayed them is why they were kept around. And if so, if normal SOLDIER's loyalty is questioned, what exactly is ensuring the greater loyalty of Deepground? By all rights, those recruited into Deepground are treated a great deal worse then those recruited into SOLDIER.
Case in point Rosso: Her killing thousands of her own men was not something unusual with her, it was just her continuing on with her day as always. The Restrictors prove that they can easily kill her, their loyalty to Shinra being much greater then hers and Shinra had decided already to never ever in ever to use her no matter what, so why keep her around. How is her spending all her time in lethal training simulations thinning the Deepground ranks useful.
If they actually
want Deepground to remain small and that's why they instruct their soldiers to kill each other as much as possible, they could've just NOT made a hundred times bigger then ACTUAL SOLDIER operation or at least stopped sending thousands down there at some point. On the subject, I thought it was hard to join SOLDIER? I don't like the retcon that it was never hard, the reason SOLDIER is so small is because 99% of their applicants are drugged and wake up in Deepground and Cloud just sucks THAT much for not even getting in at all.
Then there's Weiss. This is guy is not said to be crazy bloodthirsty like Rosso or even passively a hazard to be around like Nero. They're just afraid of him because he's too powerful. So they keep him drugged up, chained up to a Mako Reactor and inject him with a Virus that'll kill him if anything happens to the Restrictors and the main computer. Now given that they have done all this stuff to him, again I ask why don't you just kill him? The fact that you have done all this stuff to him clearly proves that you can. Despite somhow possessing all the Tsviets abilities save Nero, Weiss is calld the pure for being relatively untampered with. As proof of a successful expriment, he holds
less value then Nero or Rosso.
Not that you know, they ever tried to recreate Nero, Rosso or Azuls ability in someone they haven't proceeded to treat like dicks or anything.
But here's the really weird part, in spite of not even trusting Weiss to be concious and merely confined to Deepground like Rosso, they do actual make use of him on rare occasion. They wake him up, unchain him, give him a mission, and send him on his way fully expecting him to come
back despite having pretty much the worst quality of life of any Shinra employee ever, and that's saying something. Did the chips in their necks have such amazing wireless systems that they still receive inside even Nero's Darkness dimension?
Lastly I feel Deepground as a whole undermines the end of FFVII. Midgar was supposed to not be habitable anymore and Mako Reactor unusable. But here comes along an vast innummerable army that uses Mako to sustain themselves daily and have been living underneath Midgar for three years. And they brought a vast Armada of Mako-powered helicopters and spiderbots along with them.
