OVERVIEW:
{Etali, Primal Conqueror} can be built around in a number of ways. Ramping into it quickly obviously leaves the possibility of you hitting your now almost useless ramp. You should of course have a good amount of high end with an immediate effect on the board, but neglecting ramp and thus consistency and speed is not a real option; you can only really maximize the value you get out of your ramp. {Azusa's Many Journeys} for example does more than just ramping. {Katilda, Dawnhart Prime} often adds additional mana immediately since there are many humans in the deck and is a good mana sink when {Etali, Primal Conqueror} inevitably gets killed off; and hitting a {Reckless Impulse/Wrenn's Resolve} off of {Etali, Primal Conqueror} never feels bad.
... And yes. {Titan of Industry}, after long consideration and testing and despite it performing well, didn't make cut even in the sideboard. I know, I'm sad, too, especially since it is interaction. It's not legendary and feels way too defensive for 7.
RAMP PLAN A:
{Azusa's Many Journeys} keeps you alive, let's you play extra lands with {Augur of Autumn} and {Reckless Impulse/Wrenn's Resolve}, aswell as a land count of 27 and is found, hopefully, on turn 1 with {Commune with Spirits}.
{Thalia and The Gitrog Monster} does the same thing on the following turn, going t2: 3 tapped mana, t3: 5 tapped mana, t4: 7 UNTAPPED mana, optimally of course.
RAMP PLAN B:
Initially {Gwenna, Eyes of Gaea} was plan B on it's own, became plan C before it was cut entirely.
Now {Katilda, Dawnhart Prime}, as a 2 drop that hopefully gets you to untap for 4 next turn still keeps the turn 4 {Etali, Primal Conqueror} hard cast dream alive. Also, all creatures below cmc 6 are surprisingly humans ("Human God"? "Human Frog Horror"?!), even {Azusa's Many Journeys}' flip side. Finally, it is legendary and thus makes {Djeru and Hazoret} more reliable and isn't a horrible hit off of... "them" or {Etali, Primal Conqueror}. And that's just additional upside; I just need more ways to get to 4 on turn 3.
RAMP PLAN WITHOUT {Thalia and The Gitrog Monster} ON TURN 3:
Just play your {Reckless Impulse/Wrenn's Resolve} and {Augur of Autumn} hopefully on turn 3 without having made a land drop. That's just good old mid game card advantage at an insane, yet non-deterministic rate. For {Augur of Autumn}, 30 (+1) cards in the deck (!) can manipulate the top of the library.
{Djeru and Hazoret} both cheats out {Etali, Primal Conqueror} and is great off of {Etali, Primal Conqueror}, too, both especially when it has haste. Making lots of land drops often gets you there quickly and all your card draw is either immediately cast/put into play ({Augur of Autumn}) or exiled for 2 turns ({Reckless Impulse/Wrenn's Resolve}).
MANA:
The mana base is probably not 100% mathematically optimized, but has never failed in any way that made the deck unplayable; sometimes different sequences of plays had to be made because of color restrictions but it still felt like solid value.
The deck naturally started out R/G, adding white for {Djeru and Hazoret} and eventually black for {Thalia and The Gitrog Monster}. A 4 color mana base is usually difficult to support, but the deck being VERY much base R/G (no more than 1 B or W mana symbol on any card in the main and side combined) and tri-lands being a thing it's not as difficult as one might assume. The most important part is playing many lands (27 here + 4 {Commune with Spirits}) and thus having many different options when it comes to which land to play.
With a sub-theme of 16 legendary creatures in the main, {Plaza of Heroes} becomes insanely strong. Same goes for the channel lands of each color except for red.
The 8 tri-Lands are always R/G and generally insanely strong on their own. Probably one of the most powerful plays in standard on turn 1, they are also great after tapping out for {Azusa's Many Journeys} or {Thalia and The Gitrog Monster} (and even {Augur of Autumn} after peeking at the top) in this deck, specifically. Also cycling in a deck with a lot of lands is even more value because of variance and incidentally turns on {Kroxa and Kunoros}, too.
Pain dual lands are necessary since fast dual lands ("tapped unless [...] 2 or fewer other lands") are unplayable in ramp decks. It's not as bad as it seems, though, since all but 7 cards in the main and side combined have generic mana requirements. They usually only hurt you until turn 3 or 4, if at all.
The mana base is definitely one of the more difficult ones to play optimally and requires more attention than usual.
CARD ADVANTAGE:
You have to play {Reckless Impulse/Wrenn's Resolve} in this deck to see how surprisingly insane it is. This is the card that allows for some of the more broken turn 3 or 4 plays apart from just being a very efficient consistency tool; a problem ramp decks face, traditionally. I played 6 copies for the longest time and felt like 7 to 8 would be a reasonable choice to make. Even playing it on turn 2 (!) often is really good, looking for more land with 2 {Azusa's Many Journeys} in hand for example. Yes, you're gonna exile some of your high end stuff forever sometimes, but in that case you really needed to go those 2 cards deeper anyway. 2 mana for 2 cards was always considered very good; some vintage control decks ran {Night's Whisper} for years, mostly because they were able to cast it among other things in the same turn due to all the mana available in that format.
{Etali, Primal Conqueror} in multiples is never bad but for each other legendary creature besides {Kogla and Yidaro}, that's not the case. At least {Thalia and The Gitrog Monster} lets you turn them into rather expensive card draw when drawn in multiples, including the ability to sacrifice it to itself.
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Sideboarding:
{Haywire Mite}: Flexible vs. a) artifacts/enchantments b) aggro: chump, sac to gain life before damage, exiling some random saga
{Silverback Elder}: Flexible vs. a range of midrange decks aswell as just being game ending against aggro, topping off the life gain curve at 5. Good against artifacts/enchantments and big fliers, since the deck has neither reach nor flying. Reasonable in the main, since both {Etali, Primal Conqueror} and {Djeru and Hazoret} let you cast the cards you find, triggering {Silverback Elder}
{Kogla and Yidaro}: Flexible vs. a) artifacts/enchantments but uncounterable and replacing itself b) midrange to pick some problematic stuff off - that's why it's in the main twice
{Thalia, Guardian of Threben}: Classic backbreaking hate and/or just removal bait for the early game
{Elesh Norn, Mother of Machines}: Mostly against the {Etali, Primal Conqueror} mirror and {Breach the Multiverse} and obviously very strong, situationally. Additionally it's just a ton of value with a good portion of the main deck's high end (7 cards main deck)
{Drana and Linvala}: Situationally insane. Creature based ramp comes to mind
{The Dragon-Kami Reborn}: 4 more life against aggro and soft-locks them from attacking on the ground when it flips until they have lethal in one attack, which you are able to delay further and further. Can also be found with {Commune with Spirits}
{Nahiri's Resolve}: Only there for decks that rely on sorcery speed removal like wraths. You get to attack immediately with every creature, getting at least some value. If the trigger gets to resolve, even a {Farewell} on enchantments will not prevent creatures from entering next turn (without haste, but) probably triggering some ETBs (11 cards main deck). Be sure never to exile your opponents' permanents under your control that way, though ;) Can also be found with {Commune with Spirits}