This is indeed a client issue. Hopefully it will eventually be changed.
As far as when it was moved, I *think* it was when the classic (velious) UI was no longer useable. This came months after Luclin release though. Opting to use the Luclin UI from the beginning, I believe, would have shown the guild tag beneath the name.
Still using Velious UI, yet Luclin models and AA titles were present.
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I wasn't able to find a screenshot of the Luclin UI depicting players still having right-aligned guild tags.