Having never played an SX or Westfield I couldn't say but I have owned 10 Harley Bentons The basic PB-20 I preferred to the Squier Affiniity P-bass,it has a Poplar body
same as some of my Peaveys. Young lad at Stirling Uni uses it now on his symphonic metal recording tuned BEAD. BZ-4000-NT which is the top tier series was another good bass,
build quality and features were fantastic, JB-75 is a nice jazz bass,HB-60 performed like my last semi hollow.
Honestly I've yet to play a bad HB bass, no complaints on the RB-414 itself but the Ric inspired design wasn't for me.
The reason they're so affordable is not so much cost cutting but lower profit margins + high volumes of sales. Thomann buy direct so there's no middle man adding his costs,no sales reps or
advertising.
A friend of mine set up a Harley Benton forum,plenty satisfied owners there an I'm sure 1 or 2 will have had Westfields or SX's. Here's the link if you fancy checking it out.
http://theharleybentonclub.proboards.com/