It's not as out of left-field as you think, considering Gjallarhorn's track record.

After winning the Calamity War, Gjallarhorn put restrictive measures in place to maintain the peace. Only Gjallarhorn can manufacture Ahab reactors because they've kept the secrets to those a secret, and even then they've lost the ability to make two reactors work in harmony with each other like we see in the Gundams. This prevents other factions from being able to make their own armies of MS, resulting in MS combat being pretty rare prior to s1. Hell, the Graze was actually not designed with MS combat in mind according to the manual, most they were expecting it to fight against were the odd mobile worker which would lack the benefits of Nano-Laminate Armor because those things don't have Ahab Reactors.

AV-Implants that could give kids piloting abilities above those of trained soldiers in no time? Gjallarhorn made it so body modifications, even in the case of artificial limbs, were looked down upon.

Gjallarhorn were expecting their Graze to be the apex predator of its time. No one else could manufacture Ahab reactors like Gjallarhorn resulting in them having the larger force, and it would be seen as blasphemous to give kids AV-surgery (...oh, and fact it's for child soldiers.). Danslief were not needed in the current world until someone could step up to Gjallarhorn, but they still put a ban on them anyway in case anyone got any ideas.

And really, despite the power of the Gundams we saw the fact is most of them were listed as MIA or destroyed by war's end. Out of the original 72, only 20-some were accounted for afterwards. There's also the fact they were also trying to produce MS other than the Gundams at the time like the Grimgerde or Teiwaz suits (they were made from blueprints from that era according to the manuals). The Gundams don't appear to have been enough, so there had to be something to have tipped the balance in mankind's favor.