t's just flat-out against the rules.
As was using mixed faction dials. There were pages and pages and pages of people making excuses for why that rule was appropriate, prattling on about nonsense like confusion and aesthetics. If you are in the mood for seeing what an authority can drive people to justify, go give them a read. Now, FFG acknowledged that the mixed faction dial rule did not have a meaningful impact on the game, and I am yet to see a thread complaining about have the reversal has negatively impacted their experience. The indignation of not have originals of each card is the same. It does not impact the gameplay and has a negligible impact on players experience (which is probably outweighed by the freedom that it would bring to list building). The only difference is that FFG will not change their position because it is a much stronger force in driving sales.
Mixed faction dials have NEVER been against the rules. There was a question about how they might work and someone gave an opinion which many ran with as being 'official' but it never actually was.
It's also a completely different kettle of fish. Whether the dials match faction or not, you're still using official product released by FFG that has been bought and paid for. Copies of upgrade cards printed at home by a player are such a different issue that I cannot believe it's even been brought up.