Let me make this clear before I continue...I certainly agree with what you are saying. But "savage" is a hard work to shake off. Its possible she meant what you are saying, but I think the point she was making is that their techniques are a bit more brutal and cold than other clans. It seems she was focused more on the "way" they do things rather then their actual nature. So, to me, it doesn't really matter what exactly she said. "Brutal", "harsh", "savage", whatever she used was only directed towards the clans techniques...not the clan itself. At least that's how it read to me...
In anyways whether harsh or savage, their techniques were both. Notice that their sealing techniques were used to restrict the freedom of other entities which naturally they should be free. Restricting someones freedom, forcing it against its own will is kinda savage and harsh, but it needed to be done. Notice when she was talking about that, it was in the context of tailbeast and Fūinjutsus.
Which means SDO and TWG, both harsh or savege either is ancient or rough is still the same in that context.
It also ignores the fact that even if they were "not so nice" Rikudou's path was to follow peace. He would not have wished harm upon them. This calls into question his oracular abilities. You can extend that into the elder/younger son selection scenarios as well for that matter
Rikudou had a different view of how to attain peace in relation to his clans views. Thus as his clans sought to keep their way a secret,ie. how to manipulate chakra and their sealing abilities, Rikuduo thought that the way of peace to the world is by people knowing how to manipulate chakra. Thus after hime realising how to do it by means of the juubi, he taught it to the world. The world in its harsh and wickedness sought to misuse the art of ninjustu also and that resulted in even massive massacre which led to the dwnfall of his clan too.
This could be realise as he chose his younger who sought love with ninjustu over power with ninjutsu for the older brother.
So Rikudou had a positive outlook of ninjutsu practice in the world but it was misused by humans.