I can't give you a comparison with any of the manufacturers you listed, sorry

But I do have a set of the WGF Celts and a bunch of Warlord's plastic Celts, and snapped a quick comparison of those two ranges, which may be helpful?

As you can see, I'd say scale-wise they're pretty compatible, although the WGF ones are noticeably less detailed. They do come in some nice poses, though, whereas while dynamic, I found the Warlord set to get a big redundant.