http://www.bbc.co.uk/news/uk-politics-27177265

“As we often said, if ‘atheist’ is a meaningful category, then ‘theist’ is.”

The operative word there is ‘meaning’. It’s always the court of final appeal.
What does ‘meaning’ signify?

[“Derrida: I try to write (in) the space in which is posed the question of speech and meaning. I try to write the question: (what is) meaning to say? Therefore it is necessary in such a space, and guided by such a question, that writing literally mean nothing.” Derrida, Positions]

The problem isn’t meaning in itself, but the evaluation of meaning.
For instance, an atheist would agree with you, saying that ‘theism’ comes under the category of ‘nonsense’, ‘mythic fantasy’, the absurd’, etc..

[“Not that it is absurd in the way that absurdity has always been in solidarity
with metaphysical meaning. It simply tempts itself, tenders itself, attempts to keep itself at the point of the exhaustion of meaning.” Derrida, Positions]

The ‘atheist’ grounds himself, essentially, in a structure of easily verifiable referentialities, ‘empirical presences’ Derrida might say, & refuses to consider anything beyond what such a structure, & its logics, readily, & (demon)strably, suggest. Anything beyond his favourite (interpretative) structure, out of the purview of his ‘Reality’, he scornfully dismisses as meaningless, nothing.

[“To risk meaning nothing is to start to play, and first to enter into the play of differance which prevents any word, any concept, any major enunciation from coming to summarize and to govern from the theological presence of a center the movement and textual spacing of differences.” Derrida, Positions]

‘Reality’ is just a selection of preferred or persuasive rubrics constituting a regime, a disciplinary litany configuring worship of that arcane god, BetterOff. Knowledge of this god, & application of said knowledge, is helled (sic) to lead to an apotheosis, an identification with BetterOff, an ecstatic business.

“Carpentry has nothing to do with it – the “joint” refers to a natural point of separation for use in defining subsets of things.”

I knows, was a bit of levity.
Was trying to hint that the hunt for micro-categorical precision might be misplaced when it comes to ‘religion’. Not that one shouldn’t try, but it’s unlikely to give clarity, but who knows, I can sense a route through that, that could work, but it’s not necessarily the best or easiest way, & would require detours through more general consideration, anyway, if it’s to work. Really, one shouldn’t neglect anything, but there are more efficient ways. We’re all different, though, different routes for different folks.