THEORY: languages without arguments

I've read in several places the idea that in radically head-marking,
polysynthetic languages like Mohawk, all full noun phrases are adjuncts;
the only arguments are the agreement-marking affixes on the verbs.  (If I
understand correctly how these terms are defined, an argument is _required_
by the verb, whereas an adjunct is optional.  Thus _all_ full NPs in
languages of this type are optional, and many sentences consist of nothing
but a verb.)

Has anyone ever proposed a similar analysis of languages like Japanese, in
which all NPs (except predicate nominals) must be objects of adpositions?
In other words, the immediate constituents of the verb phrase are
adpositional phrases rather than noun phrases.  To me, this makes it sound
like all NPs are oblique, which in turn makes it sound like they're all
adjuncts rather than arguments.  (Especially since in Japanese, I have the
impression that basically all NPs _are_ optional.)  But then, are there any
arguments at all, given that there's nothing in Japanese even remotely
corresponding to the verb-agreement affixes that are arguably the "real"
arguments in Mohawk?

In some ways, Japanese seems like the exact opposite of Mohawk: its verbs
have no agreement morphology at all, and its nouns all have postpositions
to mark their case roles, while Mohawk nouns have nothing to show their
case roles except the very elaborate agreement morphology on the verb.
Japanese is radically dependent-marking, while Mohawk is radically
head-marking.  Yet somehow they both end up with noun phrases that are
never mandatory and don't look like arguments.

ObConlang:  The reason I'm wondering about this right now is that I've just
started thinking about revisiting one of my older conlang ideas, which
started out as a sort of "inverse Japanese" (basically like Japanese only
verb-initial and with prepositions instead of verb-final with
postpositions).  (When I first got this idea, many years ago, I didn't
realize that lots of natlangs, such as Tagalog, more or less fit this
description; I thought I was onto something really new.)

- Tim