I think you're getting too hung up on labels. 3D. 2D. It's all art, in the end - and 3D may be how something's modeled, but 2D is how it's usually displayed. Arguing seems silly. The only thing that really matters is that the end result is the best it can be, no matter what tools you employ to get there. Sure, in some specialized online galleries they might try to make the 2D-3D distinction, but in the real world an art director (or anyone that has their head screwed on straight) isn't going to reject an image because it was made with such-and-such a tool. They may reject it cause it looks bad, but that's something else all together. And an art show isn't going to toss someone out on their butt because they embedded sawdust in their acrylic to achieve a certain effect.

"by not using postwork you are limiting yourself"

That's true. Or at the very least what you can do with postwork in 10 minutes may very well take 4 hours if you're committed to modeling it, instead - and the results may be identical. Anyone can choose to stick to just 3D if they really want.... I just don't understand why they'd want to if empoying other tools could save them time and potentially improve the final image.