This claim loses significance when you consider 70% of Ethiopia's water resource is in the Nile basin. There is no development without using that water.
Yes, but those sources, in many cases, are also source of the Nile. I mean, as a matter of hydrology, it's a basin. Unless you're implying that they can only take 12% of the flow of Nile tributaries, but would be free to take 100% of the flow from lakes that feed the Nile tributaries? Somehow, I don't think that's what the colonial treaties meant. I'm pretty certain any draw down of flow from Lake Tana for instance, would also violate the treaty. Definitely any draw down of flow from Lake Victoria would be a violation. There's no way the Sudan and Egypt would be OK with that.
Yes but that seems irrelevant to who should get to use it. That’s not how the wealthier Northern African states have treated other scarce resources like electricity or food during droughts.
Now that one of the poor upstream states wants to use the water passing through their backyard to tackle these issues, the most important issue is who needs a given resource more?