I'm not doing that Mah exist(s/ed) but the reasoning behind coming to that conclusion was poor.
I kind of dislike how Jmods release information/lore not gainable from in-game. Kind of ruins the suspension of belief and the immersion into the world when the player can act like a God and know things the player should not know in game.
For instance, with Sliskes' mastery of shadows - what if "Zaros" was just one of his puppets and he is using this "Zaros" to control the other Zarosian Mahjarrat for his own benefit so that he can rise to become a new god? And he is trying to do so without the Stone of Jas so he is getting the gods to fight amongst each other in hopes he can claim an elder artefact for his true ascendancy. He doesn't want to make the Dragonkin stronger by using the Stone because he has already seen what happens to a Mahjarrat who uses the stone before ascending to godhood (Lucien, unlike Zamorak who is still alive)
Well... that's ruled out because Jagex has explicitely stated that Zaros is Zaros and that Zaros will be returning in the next quest.
Kinda... kills the fun of speculation.
Y'know what else kinda ruled that out?
Zaros being referenced as a God in the god letters and in cryptic in-game stuff prior the the Mahjaratt even existing as a concept within the game and well before they were given any tie to Zaros.
Zaros as the 'dead' must not be spoken about god is a fact left over from the Andrew Gower original lore, back when Sara, Zammy and Guthix were 3 brothers who claimed to have created the world.
God letters are not strictly canon. Guthix's mannerism of speech and referring to the other gods as "brothers". Saradomin calls Guthix his brother, which could be seen as a priest/Christianity relation thing, but why would Guthix call Saradomin or Zamorak "brother"? Oh, I have the answer for this though.
As to thy secondary question, the term of brother towards my fellow deities is an honorific rather than a familial one, for our past ancestrys are mightily different, yet I call all deities on this world brother or sister, for this is the closest term that humans have to describe our relationship.
Except in game he does not refer to them as "brother" but rather by name directly.
I hath no race, I am unique in all of the worlds. I am simply Guthix.
Naragi. As well as being "unique in all of the worlds' ... except the Naragi homeworld of course.
One full year of this planet is the equivalent of one heart beat for myself, although the parallel is flawed for I hath no heart and do not breathe
"I feel my heart grow heavy and my breathes grow longer."
But I hope Guthix was right and the God letters are canon.
I exist because I must exist; if I did not, then I would be created again, for the universe requires balance in all things.
Because then he isn't really dead.
Oh but Jagex themselves says they are non-canon:
The God Letters were written for fun and the information contained in them is not to be considered canon unless otherwise mentioned.
Yes the God Letters are not strictly canon but the example of Zaros must not being spoke of does not contradict any more recent additions and is the most finite example of the concept so there is no reason to not use it as an example point, especially as I even referenced the fact other in-game stuff follows the same line and that it was a leftover from the god letters lore days.
They are a perfectly fine source for filling in grey details as long as you do so with the awareness that anything newer entirely supercedes them and is not a contradiction. The same as pretty much any fandom universe does - non-canon sources are allowed to fill in grey details, as long as said detail does not contradict anything from the official canon and is only valid so long as this remains true.
Also side bar your point about the 'I have no race' comment is invalid. It is established in the current lore gods have no race and they stop being of their race as soon as they ascend. Guthix was not a Naragi, Saradomin is not a human, Armadyl is not an Aviansie, Zamorak is not a Mahajaratt, Marimbo is not a monkey, Brassica Prime is not a cabbage. They originally were these races/things but after ascending they are not anymore. Plus his being unique in all the worlds is not an issue either - he was the only Tier 2 god to have ascended instead of being created making him unique and he was the only Naragi origin god as all the others died so he was unique in that respect too. Where as other gods are not unique due to sharing tiers of ascension and most if not all of them their origin race still lives so they could be made less unique by another ascending. So all told that passage holds up even in todays lore.