They don't really compete on quality even. Quality is high in some ways. Their soldermask is tougher. But for instance alignment between drill/copper/mask/outline accuracy is no better. And all the chinese fully route the board outline, you have no cleanup to do. oshpark leaves panel tabs at random places all around the board that you have to grind down yourself. A big deal if the pcb is a special shape to fit into something else. I have one that is under 1/2" square with a funky dog bone or T shape. Not only do they allow it, they route the whole outline. idk how they can even hold onto the board physically to do it.

oshpark puts panelization tabs right in the middle of a row of castellated edge contacts.

And they often take longer to ship to me in NJ than Elecrow, a shop that's even cheaper than jlc or pcbway, without even using DHL, just the cheapest shipping.

Never mind the lack of features. I have a board that needs 1.2mm pcb. Well on oshpark I guess I can make 0.8mm work. 3d print a filler plate or something. But what I really need is 1.2, and all the chinese shops have it, not even special extra cost, or maybe barely.

15 years ago oshpark was great.