I do agree that it probably makes sense to err on the side of being too quick to estimate that something is likely sapient than to err on the side of being too

I do agree that it probably makes sense to err on the side of being too quick to estimate that something is likely sapient than to err on the side of being too slow to do so. However, that doesn't make it impossible for a plan-producer to be both superhuman and non-sapient. Nor do I think the default is for an AGI to be sapient. (Though, possibly the default could be such that it isn't but in a way in which we couldn't be sufficiently confident that it isn't, and therefore be obligated to behave as if it is sapient) But, in the FOOM scenario, I would expect that "whether or not to treat it as if it has rights" would be the least of our worries. (the greatest of our worries would be, roughly, "whether it kills everyone".)