Edit: This is not an answer to the question, but a pointer to the solution of a different problem (due to a misunderstanding on my part)
I'm not an expert on this, so possibly misunderstood something, but to my mind your result on ultrametric spaces appears to badly contradict Theorem 4.2 of a paper by Louveau and Rosendal, which says that the quasiordering of embeddability for Polish ultrametric spaces is a universal analytic quasi-order (for Borel reducibility), which implies that it is very far from being wqo.
The paper in question is available here: http://homepages.math.uic.edu/~rosendal/PapersWebsite/CompleteAnalytic.pdf