Xerocomus spadiceus, aka Boletus ferrugineus (a still valid name that IMO should be deprecated due to it not being a porcini to begin with, not to mention the fact the two names may represent two different taxa both in Europe and in the USA), is likely to be a member of X. subtomentosus group together with other North American taxa, such as X. tenax and X. illudens. Since X. subtomentosus is the type species for the genus Xerocomus sensu stricto, the “dust bin label” X. subtomentosus group makes enough sense to broadly represent all phenotypic allies of that species. What doesn’t make sense is creating an artificial group label centered around a bolete having a taxonomic and nomeclatural position in need of verification.
I am not aware of Xerocomus having been studied extensively on the phylogenetic front. According to a massive nrLSU phylogram of the Boletaceae associated with Nuhn et al. (2013) paper, X. subtomentosus, X. illudens and X. tenax are all bona fide Xerocomus. A X. spadiceus voucher (G.B. acc. #AY612842) nested in Xerocomellus and is likely to be a misidentification.