I think we need to focus less on the arbitrary division that's been created with PDs when it comes to clusters. The DSM itself notes that the grouping of PDs into clusters is only for research purposes. This is what the DSM-5-TR says in the PD section:
"It should be noted that this clustering system, although useful in some research and educational situations, has serious limitations and has not been consistently validated. For instance, two or more disorders from different clusters, or traits from several of them, can often co-occur and vary in intensity and pervasiveness."
The PDs within each cluster have similarities, yes, but they're not dissimilar from the PDs in other clusters. SzPD has a lot in common with StPD but also with NPD and BPD and OCPD and AvPD - none of which are in the same cluster A. There is no significant meaning behind cluster groupings, don't treat them like there is.
