Yes, this is the typical Buddhist outlook. At the same time, I suspect lots of Buddhists throughout history have felt uneasy about this, especially the educated ones. I mean, it just doesn’t stack up. But then the forces of culture have stifled these alternative voices. What this means is that I don’t think it is impossible to change the narrative. Once the case has been properly made, I expect the floodgates to open. The message just needs to be repeated until people get used to the different perspective. Standing outside of traditional Buddhist societies, we have the luxury of not being subject to the same cultural forces. This means we have a responsibility of saying unpopular but necessary truths.
I prefer the former understanding. The latter view seems to be rooted in suttas such as AN8.8, which has been shown by Bhante @Sujato, here, to be late. As I have shown above, the Buddha seems not to have agreed with this.
In theory, I agree that anything that agrees with the word of the Buddha could be considered Buddhavacana. The problem is that it is often hard to judge whether there is real agreement or not. The discussions found in the Kathāvatthu are enough to remind us how hard it can be to discern the authentic from the inauthentic. The easiest solution is often to leave aside anything that is even remotely problematic. There is plenty enough to reflect on in the early suttas.
It is perfectly possible to reduce defilements through the wrong means. For instance, indulging in sensual pleasures will lead to a temporary reduction in craving. But I am sure we can agree that this is not the path recommended by the Buddha. Similarly, powerful faith in a creator god may reduce the defilements, but will block you further down the path. And so a reduction in defilements is not a sufficient criterion to decide what is Buddhavacana. (It is interesting to note how we are already disagreeing. Sticking to the word of the Buddha will minimize such problems.)
Only when the Buddha gives his stamp of approval. Then, of course, it is as if it was spoken by the Buddha himself.