This isn't as daunting as it seems, and the key for me was Eyedol. His Titans Vengeance perma bonus that allows him to take less damage from projectiles and walk through them is crazy helpful for making it through all four Omens and Gargos without any deaths.
In getting to Gargos I started a new game on Normal and tried to control the corruption from zone to zone to get one Omen at a time to ensure I could use Eyedol on each one. I also made sure to skip every shadow mission as you never know how good the shadow you're going to fight will be.
For the Gargos fight with Eyedol I used the following setup:
- Killer Watcher Guardian. Use whatever your best Guardian is for the Attack and Defense boost.
- Dragonskin Nanobots Mk III for +25% Defense
- Myogene Nanobots Mk III for +25% Attack
- Embalmed Lizard Foot to prevent Gargos from getting too much instinct and shadow if he gets off a combo, but I don't think I ended up needing it.
- ARES Battle Stim Mk III for constant Shadow refills during the match.
So with the +100% Defense and +105% Attack from the guardian and nanobots I was able to nearly kill him with a perfect victory and I'm not very good. Using the combo assist I was able to pretty easily mash my way to a simple victory.
I actually found the Omen fights more challenging than Gargos, but I also didn't use the nanobots for those fights.