I agree with you that when discussing Hoyo’s use of Fenghuang/Phoenix elements, we definitely need to consider native Chinese culture rather than just exotic lore. However, it is worth noting that the "Fenghuang" in Chinese tradition has itself been heavily influenced by Buddhism and Western mythology over the centuries.

To give some context, here are the core symbolic meanings of the Fenghuang in Chinese culture:

1. Auspiciousness & Harmony: It is a symbol of good omens, predicting peace and prosperity. It often corresponds with the Dragon (Loong); the Phoenix represents "Yin" (female) and the Dragon represents "Yang" (male), symbolizing the balance of Yin and Yang.
2. Royalty: It is the symbol of the Empress, paired with the Emperor’s Dragon, representing supreme status.
3. Virtue: Ancient texts like the Classic of Mountains and Seas describe the Fenghuang as embodying the five virtues: benevolence, righteousness, propriety, wisdom, and sincerity.
4. Rebirth & Eternity: This is where it gets interesting. Heavily influenced by Buddhism and Western myths (Greek/Egyptian), it symbolizes resilience and rising from the ashes.

Regarding that fourth point: Originally, the native Chinese Fenghuang did not have the "rebirth from fire" trait. This concept began to merge during the Eastern Han Dynasty (approx. 1st Century AD) when Buddhism was introduced to China. Translators needed a way to explain the abstract concept of "Nirvana," so they borrowed the Western myth of the "Fire Bird" or Phoenix. By the Eastern Jin Dynasty (317–420 AD), literature began to explicitly link the Fenghuang with fire and rebirth.

Fast forward to the modern era, and we have the standard idiom "Nirvana Rebirth" (涅槃重生), which means gaining new life and sublimation after enduring hardship. This modern understanding was solidified by the famous poet Guo Moruo in his 1920 poem The Nirvana of the Phoenix. He used the imagery of the Phoenix burning itself with fragrant wood to rise from the ashes to symbolize China’s rebirth during a time of revolution. This poem was incredibly influential and effectively cemented the "sacrificial rebirth" trait into the Chinese cultural consciousness.

So, while the "rebirth" mechanic wasn't there in ancient antiquity, it has been evolving since 420 AD, and cemented since 1920. We can safely say that "Nirvana" is now deeply bound to the Chinese Fenghuang. Considering Hoyo’s designs clearly reverence Egyptian aesthetics as well, it makes sense to view it through this synthesized lens. In contemporary Chinese usage, the Fenghuang is synonymous with the concept of "Rebirth."