Not so. The argument is that certain types of claims are impossible - those involving new, long range, strongly interacting forces. (Which is equivalent to saying new particles, since these are just the force carriers.)
What is not impossible is unknown properties that arise from existing forces. My go-to example is high temperature superconductivity - it was surprising, unforeseen, and puzzling - but not a violation of QFT. Certain claims are definitely ruled out, but this doesn't eliminate new phenomena.
And that's true. So any explanation has to use the known forces. We can say, with authority, that inventing magical stuff like "morphic fields" is bogus.
The problem is when a new phenomenon is demonstrated (if it is, which was the working hypothetical) - can it ever be proper to deny the phenomenon exists on this basis? No, I don't think so. What is required is an approach that narrows the realm of possible explanations without claiming something cannot occur because we haven't yet figured out how to fit it into QFT.
The onus is always on the theory to fit the world; the world has no duty to follow the theory.