The link between Titans, lyrium and sources of magic

If the "Sun" was a Titan and elves were originally spirits of the Fade that took on material bodies, it is entirely possible that Elgar'nan saw it as his father because it was associated with the material world from which he took his body. This seems confirmed by the legend where it states he was formed at the point where the Sun touched the Earth, the boundary between the Fade and the Waking World perhaps? I would just mention that in this elven myth of creation Elgar'nan does not kill his father but effectively subdues and imprisons him. He was angered by its destruction of the things created by the Earth for his pleasure. Perhaps the Earth is symbolic of the ordinary elves as this would then fit with the plea from them to take vengeance for the destruction in the Song to Elgar'nan. Then Mythal intervened and negotiated a peace that would allow the "Sun" to be restored but on certain conditions. There was a story about her creating the Moon out of the area in which the Sun had lain. Also, the blood of the Sun was scattered across the sky during the fight and Mythal was born out of the sea of the Earth's tears. The Dalish legend just got a few of the details mixed up in their half remembered myth, so they have the Sun opposed to the Earth, when in fact it was Elgar'nan, the Firstborn of the Sun, who fought the Earth/Titan.

These various references to blood, sea and tears, could all be referring to lyrium in one form or another, although the Sea could refer to the Fade. I've long thought the scattered blood could refer to the various solid lyrium deposits throughout the Deep Roads that are effectively dried blood. Mythal's creation of the Moon likely refers to her collection of lyrium and likely was the basis for her cities, may be even the Eternal City in the Sky, which may have had a counterpart in the Deep Roads. My instant reaction on seeing the interior of the Titan in the Descent was to think of an elven city with its floating walkways. So, essentially, instead of referring to the actual Sun, Moon, Stars and Earth, as you say, the legend is telling the story of Elgar'nan and Mythal's conflict with the Titan(s).

Of course, there is another aspect to the religious symbolism and that is the Maker. Leaving aside the writers declaration they would never prove his existence or discredit it, there is room for the Maker of the Chantry not necessarily be the actual Creator of everything. Also, the attack on the Sun could originally refer to Elgar'nan rejecting the Maker and rebelling against his rule. So, the Sun was responsible for the creation of Elgar'nan the first elf when he gave a material body to the spirit. This then got mixed in with the later story of the war with the Earth in the Dalish myth. There is also the possibility that the Golden City was originally the home of the Maker but he withdrew not at the approach of the Magisters Sidereal but the much earlier attack by the combined might of the Evanuris.

Mind you, the Golden City could just have been a reflection in the Fade of the interior of the Titan in the Deep Roads, turning Black within as its counterpart did but the golden illusion was maintained in the Fade so long as it was only viewed from outside. Then when the Magisters Sidereal broke in the illusion was destroyed and its true nature was revealed. Meanwhile, they found themselves in the actual city in the Deep Roads.