The "object and array need to be entirely and deep parsed" and "object and array cannot be streamed when writing" are somewhat incompatible from a (theoretical) parsing perspective, though; you need to know how far to skip ahead in order to do so.
I agree that it is silly to design an efficiency-oriented format that does neither, though. Ion chooses to be shallow parsed efficiently, although it also makes affordances for streams of top-level values explicitly in the spec.
https://amazon-ion.github.io/ion-docs/
The "object and array need to be entirely and deep parsed" and "object and array cannot be streamed when writing" are somewhat incompatible from a (theoretical) parsing perspective, though; you need to know how far to skip ahead in order to do so.
I agree that it is silly to design an efficiency-oriented format that does neither, though. Ion chooses to be shallow parsed efficiently, although it also makes affordances for streams of top-level values explicitly in the spec.