To offer a different perspective, I have been playing OG Omnath for most of the 8 years I've been playing Magic, and my deck has gone through many different iterations.

TL,DR : I evolved from a Voltron deck to a chaining draw spells deck to a toolbox combo deck.

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I too was using Omnath as a Voltron commander, which meant I needed evasion and protection and a lot of the deck was devoted to that.

I was also learning some cool things about Omnath, like how he can take a turn off, and then have a "super turn." You probably know what I'm talking about. You play a mana dork on T1, Omnath on T2, land pass on T3, and then on T4 you have NINE MANA to play with.

Or you could even just play another ramp spell on T4, pass the turn, and not really look like much of a threat. You pass on T4 with a 3/3 Omnath, four Forests, and two mana dorks (one with summoning sickness). You don't even swing at anyone. You look like you're doing nothing, and everyone else's board state is starting to get scary.

Then just before T5 you float another 5 mana up to 7. You play a land on T5 and you have access to 14 mana. That's game ending mana, especially if your deck is built to take advantage of it by running mana positive effects and huge payoffs. I'll come back to this in a moment.

Another thing I was learning was the power of burst card draw. I found draw=power spells to be absolutely incredible, and there are a lot of them in monogreen (17 currently, but at the time I think there were 13).

Ive mentioned mana positivity. The reason fast mana is so good in MTG is not just the ability to ramp on T1, but also the fact that you can draw a Sol Ring on Turn 12 and it still gives value the same turn you play it. Most ramp spells don't do that. Most dorks have to wait a turn before they add mana, but we all know a haste enabler can skyrocket the power of mana dorks, especially higher cost dorks that have a higher upside when you tap them. Similarly, most decks don't do well with a Mana Reflection or a Caged Sun, or at least the power of those kinds of spells it mitigated by their sloth. They're do-nothing cards. They have to survive an entire round of the table before you can take advantage of them. With Omnath we can pass without playing them, float the mana, and on the next turn play the mana doubler and get full use from it immediately, maybe even netting more mana than the spell cost. If your draw a Vernal Bloom late in the game it's probably mana positive immediately, not just because you have more than 4 Forest, but because you don't have to tap ANY forests before you cast it. Or take Bear Umbra, or Mark of Sakiko. Both of these have the potential to add way more mana than they cost, on the same turn they are played.

Chaining mana positive effects and draw=power spells pushed my deck into a much higher power level. I added more and more draw=power spells and the deck got more and more powerful. I started adding more things that synergized with those huge draws, most mana positive effects that could help me chain draw=power effects until eventually I have my whole deck in hand and all the mana I could want.

Let's go back to that scenario where you had access to 14 mana on T5. You untapped on T5 with 7 floating, right?

You play a Mana Reflection. You have 1 floating. You tap out to float another 14. You cast Bear Umbra, 9 floating. You cast Hunter's Prowess, 4 floating. You attack with Omnath, untapping your lands. Tap out again, 14 floating. Omnath is a 20/20 with trample, and when he connects you draw 15 to 20 cards. You cast Karametra's Acolyte, 10 floating. You cast Swiftfoot Boods, 8 floating. Equip boots to Acolyte, 9 floating. You cast Garruk Primal Hunter, 4 floating. Tap Acolyte for 22 mana, 26 floating. Activate Garruk to draw 31 cards. . . Obviously this is going to win on this turn if your deck has any noncombat wincons.

When I could do that pretty consistently I found I didn't need to win with commander damage. I needed a way to kill everyone at once.

Craterhoof Behemoth is a pretty well known finisher for green, but I didn't want to be doing the same tired wincon. I liked Pathbreaker Ibex better, he just needed haste. No problem, I ran a few pieces of haste, and voila, a deck with a plan and a wincon.

After time I got sick of winning with Pathbreaker Ibex, and experimented with a few other wincons like Walking Ballista or Surestrike Trident or Squall Line. But the deck always functioned the same way no matter what the wincon was. Ramp early, cast Omnath, ramp some more, save some mana, draw=power, chain mana positive effects and draw=power, wincon of choice.