Check to see what order the lock retainer and retainer with the bent tang are on.  I had 2 of my EDS OX derailleurs assembled with the "B" screw tang assembled below the retaining ring and they both bound up when I would tighten them.  Swapped them to what is shown in the attached image and they swivel on the hanger when tight.

thanks, but unfortunately my EDS OX 2.0 is completely different and it doesn't have the same assembly.

You may way to list your height, inseam, and arm span.  Can't give a recommendation for sure since we don't know if you're on the short/middle/tall end of a large on the Epic.  But the large FM909 would be more comparable to large Epic, it'll feel way different though.  The reach is longer, but the seat tube angle is steeper, meaning the saddle is further forward and closer to the handlebars.  So that 30mm extra reach is negated by the steep STA.

Thanks. That's what I thought as well. Since you can't be fussing around with offset seatposts on a MTB and a dropper.

I'm 179cm with long torso and short legs (inseam of 81cm). I also have positive APE Index. I typically prefer 56cm road bikes and L sized MTBs. The Epic EVO L is definitely my size. I'm currently running the Voice Rhapsody VP4 on Large Size as well.

So they actually went with a 28mm spindle ... WHYYYYYYYY

easy conversion to DUB and 30mm BBs with the protective reducer to prevent axle from grinding against the bearings.

You still get the native 24mm support (which is super nice)

Yeah that doesn't look good.

Have you sent them photos of that as well and if so, what have they said to this one?

If they still won't replace the frame then is the oval too small or too big at the widest part?  If it is too small then it might be possible to rescue it with a drum flap sander / flap wheel.  Not ideal, and also expensive but just a thought.  Also, if you bought from Aliexpress and the seller won't come to the party then I would be opening a dispute. That's two pretty poor QC issues.

They repeatedly insinuated I was lying and finally had to "reluctantly" ask me to return the frame after I sent them two caliper measurements (pictures) and spoke in Mandarin. (I'm a Chinese from another SEA country)

These people are really the one of the worst when comes to customer service and QC in the industry.

I own many China products, resell plenty of them and it's really the truth that you get the best of the best and the worst of the worst from the same place. For TanTan Seraph, avoid all all cost.

I've lost nearly 238 USD out of this whole deal, for what is essentially a 350-360ish USD frame. The shipping cost back to them is insanely expensive.

It is hard to tell from that pic but I am assuming that is a carbon recess and not an aluminum race?  If it is a carbon recess then for me it does not appear to be a problem. Your headset will have a metal cup that will press into that recess and the bearing will then sit into the cup, the metal cup spreads the load.  That said, I would be looking from the top down into the headtube to make sure that is is only a small issue and it is not a problem around the whole of the bottom section, if that makes sense. The bottom section is often formed by bonding a smaller carbob tube into the layup of the bottom section of the headtube.  If that hasn't bonded properly then it could lead to a much bigger failure later on.

Either, it is a shame that this sort of thing slips through the QC process.

Yes sir it is a carbon recess and not a aluminum race. You're looking directly at the bottom of the head tube bottom cup itself. There is no race/metal parts being installed. This is a bare frame.

The Carbon tube seems fine. Only the recess are has a small void/hole/slit.

EDIT: Forgot to mention this is an integrated headset so there is no external metal cups being pressed in for the head tube bearings.