Is Gilgamesh that broken?? I don't really now much about his verse
Simply put, he’s among the strongest Servants in the whole setting.
His main NP is his Gates of Babylon which contains anything invented by mankind from wine to tactical nukes.
More importantly, it gives him access to every other weapon NP seen in the series that were made by man. So he can call upon his own Gae Bolg, Clarent, Harpe, Caladbolg, etc. that are just as powerful as the ones used by other Servants.
However, as pointed out by Shirou, Gil lacks the proficiency in using each of these weapons compared to their users so he’s limited to just launching the weapons as projectiles with whatever passive effects they have.
He can fire Gae Bolg and make use of its curse of causing incurable wounds for example but not its actual NP attacks like reversing causality to make a thrust impossible to dodge.
The only exceptions to these are his own personal Noble Phantasms: Enkidu, Sha Naqba Imuru, and Ea
Enkidu is a chained weapon meant for binding gods or those descended from them like Demi-gods, something Yhwach is, doubly so as the Soul King
The weapons bind and seal the opponent, and even trying to dematerialize and teleport the Servant away doesn’t work. In terms of limits, Heracles broke out of the chains while functionally dead already by breaking past his normal limits.
There’s Ea, one of the most powerful purely destructive NPs in the whole series. Gilgamesh aims the sword made of three rotating cyclinders that move with force comparable to tectonic shifts that gather massive amounts of prana and wind together before firing them as a huge pressurized blast that tears apart space and reality itself.
And finally there’s Sha Naqba Imuru which is Gil’s clairvoyance which allows him to see the truth of whatever’s before him: The person’s identity. their powers, whatever powers they have prepared, what their powers are, and any other secrets they might have, while also giving him set instructions on how to best deal with the enemy which works perfectly with his literal Swiss Army knife of weapons. It’s even wide reaching enough for him to see into the future of parallel worlds even.
Do keep in mind that sometimes his arrogance keeps him from making the full use of his clairvoyance like against Shirou due to his Faker Complex against him and Saber who he wanted to make his wife and wanted to keep her defiance against him going for as long as possible. Against both, he periodically shut off the clairvoyance enough to play with his food and end up being taken by surprise at his respective losses against them in both Fate and Unlimited Blade Works.
Bites him in the ass again in Heaven’s Feel where he gets a premonition of his death at Sakura’s hands that he’s so outraged by, he willingly shuts it off when confronting her. Predictably, it bites him in the ass where he underestimated her regeneration and gets eaten by her.
That said, against Yhwach whose both more than powerful enough to register as a genuine threat and someone Gil has no particular attitude towards, he’ll be more than willing to make use of his Clairvoyance against him.