But things could change in 300 years or so.
I'm not talking about "300 years ago" I'm talking the other Department Heads on his ship and the hero ships that we see throughout the 60-odd years of the show.
Is Scotty ever referred as Chief Scott? is Yar... Worf... LaForge... Torres... or literally any Department Head who is confirmed to also be a commissioned officer?
No, or if they were I'd bet that it's a single abherrent example among hundreds or thousands of the more consistent option.
But couldn't "Chief" be regarded as a billet too?
No. Chief of Operations is the billet, "Chief" (short for Chief Petty Officer, Chief Master Sergeant or Chief Warrant Officer as applicable) is a rank.
In that case, the Wardrobe Officer on the Enterprise wasn't doing his job.
Nope, because in universe he is wearing the correct rank insignia or rank group insignia for his rank, because the dialogue remains consistent throughout.
But it's still visible.
See above.
And aren't mine suggestions about demotions and such a little more exciting?
YMMV, but I don't find dismissing objective facts that support a logical consistent scenario to resort to bashing and half-baked speculation that can't be confirmed or denied appealing.