[rossitter]

Comparable to one use case of the passive voice, maybe.

What do you mean by "intended agent"? "Agent" has a common definition in linguistics, and an agent is only an agent in the context of a verb, not an overarching narrative. The same referent can be an agent in one sentence but not the next: "We hid. To our surprise we were found by group A." "Group A" is the only agent in the second sentence.

There may be other definitions of "agent" in other contexts, but we're talking about grammatical voice here.

The passive voice is quite simple: the grammatical subject is filled by the patient or theme of a clause, not e.g. the agent. There are many use cases for the passive voice apart from obfuscation, and obfuscation is hardly a necessary result.

I might call "surprisingly" in your interpretation a weasel word in the broad sense. The inference is that the author wants the reader to take up an attitude but is not being forthright about it.

Of course some passive clauses may be weaselly in their own right, but the passive voice is not weaselly by definition.