I do not feel in my own reading that this is what Bruno means.
He was most likely more influenced by Neo-Platonic conceptions, for one thing. In this conception, Shadows have just as much energy - possibly more. The notion of Ideal forms has been replaced with something more like pure subjectivity or “becoming.”
I suggest reading other Bruno books, particular Thirty Seals and The Seal of Seals to understand more of where he takes these matters. Reading only On The Shadows of the Ideas is a trap, and it is far from his best book.
Remember too that it was one of his first books and so much of it is a “sales letter” for the Clavis Magna, which he seems not to have written. But I think we can guess where he was going with these matters, and I’ve made some guesses at that direction that I feel are at least worth considering.