None of this, of course, involves his hydra discount. Which is pretty impressive. 4 less is huge. But...let's be honest. Most hydras are pretty terrible in commander. And while a 4-mana discount is a lot, it's also only available after sticking a 6-mana creature. If the goal is to ramp, there are certainly more efficient ways to do it, and more useful things to ramp into than hydras.
So this version of gargos is meant to use him in a different way - as a conduit for a mono-green deck to play control. Green is basically a non-starter as a control deck because of its inability to deal with creatures, but gargos shores up that weakness in a big way. He's also a very efficient win condition that can become a 2-turn clock quite easily, and even plays defense at the same time.
The deck builds a lot like feather - many cheap combat tricks and protection spells that would be a waste of a card in a normal deck become very reasonable here as a way to both protect your primary win condition and control piece, and as a way to utilize that control piece. Unlike feather, though, we can make excellent use of auras, which makes a more voltron-focused approach more reasonable.
We do, however, require some not insignificant amounts of ramp to get Gargos out ASAP, and ideally with protection up - so we're aiming for the 6-7 mana range. This is a little nebulous so we aren't committed to specific mana costs in our ramp, except that we do want most of our ramp to cost 3-4 or less, so that it helps in our primary goal of getting gargos out and letting him do his thing.