That could've caused a major wipeout on the road/trail.
Is this more likely to be a design flaw, or low quality alloy issue?

I wouldn't go as far as expert but I have a little bit of knowledge of this kind of things. If you could get some good close up photos of the two faces if you can get them apart that might be helpful. Make sure to indicate which side is the pedal side.

what kind of hardware comes with the group? ltwoo er9 comes with well over a dozen different bolts for the brakes, as well as 140 & 160 adaptors for both front and rear. In contrast it seems that shimano really skimps on hardware, which i find so incredibly $hitty of them.

Welp, I finally got around to installing it but front derailluer's adjustment screw doesn't work screw hole has its threads stripped....  Sigh.  Since I bought it off AliExpress, the options given to me where to ship it back for repair or replacement and they'll only cover $20 for the shipping.  What a pain.  I think I'll just retap it myself with larger pitch threads and grub screw to match. 

youtu.be/954JlwyqVzI