I have no issues using JW malts and use them almost exclusively as my base malt with the exception of their munich... i just prefer weyermann.
I tend to lean towards using grain from their locality for specific styles e.g. a german pilsner i will use weyermann pilsner, muncih dunkel will get weyermann munich etc.
The crystals from JW have mixed reports, but i tend to lean towards using more of their lighter crystal and a dash of thier darker over using just a 'medium crystal'. Another preference is to use Carafa Special over their Chocolate malt. Each their own really. The bottom line is if i could buy a bag each of JW Ale and Pils malt for the same price of a single bag of weyermann pilsner i would buy up on the JW for my personal everyday beers like APA's IPA's, Stouts CAP's etc. (non mainland european beers).
As a point of reference Ive made a hefeweizen with the same recipe, 50:50 pils:wheat with JW and with weyermann. The resulting beer had very little differences between the flavour profiles. The only thing i noticed was the dent in my wallet my using weyermann.
Bottom line... is JW sub standard to Weyermann? Only if you think beer has Terroir. Much like making a French Brie with Australian Milk. It might taste the same, but the underlying factor is its 'different'.