First, I applaud the lengths you went to isolate the root cause. I wish more people would do that before posting a one-sentence “need help” post.
One thing still stands out to me in your comparison: have you tried a 0.4 mm nozzle on the X2D?
In the example shown, you’re comparing the X2D with a 0.6 mm HF nozzle against the X1C with a 0.4 mm nozzle. That means the printer, nozzle, and associated profile are all changing at the same time. Since the same spool prints correctly on the X1C, you’ve done a good job ruling out wet filament, but I don’t think the test yet isolates the X2D itself.
I ask because my experience with Bambu Studio profiles outside of the default 0.4 mm profiles has been very poor. I’ve tested quite a few of the supplied 0.2, 0.6, and 0.8 mm profiles, and so far I’ve had a 100% failure rate among the profiles I’ve tested. Because of that, I now calibrate them myself rather than assuming the supplied profile is properly tuned.
Given that you already suspect the 0.6 mm profile or HF nozzle, I’d be very interested to see what happens if you put a 0.4 mm nozzle on the X2D and rerun the same material. That would remove one of the biggest variables from the comparison.