I can't even imagine an engineer @ Hodgdon would tell anyone this. So WST isn't sutiable for handgun loads but Clays is, really? One can safely make any powder work in any caliber w/ any bullet weight. Are their limitations, sure, but saying it can't be done is just ridiculous.
I used to load a ton of 452AA. When Win discontinued that powder, they came out w/ WST. I was told by the guys @ WIn it was an improved 452AA, less temp sensative, but loaded the same. So when I started using it, guess what, identical chronograph readings w/ the same loads I had been using. There was quite a bit of printed data for 452aa back in the day.
I have been using WST in 9mm, 40 & 45acp w/ varying degrees of success. It seems to give best accuracy well off the top end in 9mm & 40 w/ all bullet wts. In 45acp, I have found nothing better for any bullet wt or type, slow to pushing max.