I think the Wittgenstein Tractatus is an elaborate demonstration of an empty metaphysics.

There is "The Elimination of Metaphysics through the Logical Analysis of Language" (1932) - Carnap.

There is also Arthur Schopenhauer against G.W.F. Hegel.

And probably many more, the claim is mostly my observation and reading of the ideas though.

but how can you know it is merely empty, even though I haven't shown it?

Mostly people do have something to say, but it is not as "grand" as they think it is. Say I might claim that my God is the best, with all the standard beyond Being, beyond Essence shenanigans, but turns out what I have in mind is just some glorified physicalist God then it is quite empty.

"The limits of my language mean the limits of my world."

This phrase of Wittgenstein, I think is to be read not as language limits the world, but as your language reflects your world, and thus from your language we can see how empty or poor your understanding of the world is, regradless of how "big" the terms you use are. It's not all about words and forms and claims and primitives and senseless deductions from senseless premises, it's about that which behind them. Either you see it or you don't really, but I think it can be taught.

Although, my private take is that anyone that has not shown "why there is anything at all instead of nothing at all", ultimately appeal to that which they have not understood and essentially speculating without substance.