I was just fine brute-forcing the battle with silver sword, tower shield, Bonemass power, and fire resist wine. Used one shot of medium stamina and medium health just to make it go faster, and finished the fight well before the Bonemass power ran out.

It took me 2.5 game days to kill him.

With fire Potion u can tank a lot of damage. Yeah the fire and meteors are annoying but with good food and potions u can hit him for a while then kite him a bit to heal and hit him again. Boss is a joke like all.

I did it with Frostner and shield for example

More arrows.

throw your arrows away since they deal like 0 damage to yagluth, grab a frostner, bonemass buff and fire resist, bring a couple hp potions/stamina potions and as long as you don't get glitched inside his hitbox while meleeing him you should be able to tank almost all of his damage (while backing up to heal while getting low every once in a while). There's really no optimal way to dodge his attacks while dealing enough damage, you just gotta tank it.

Yagluth has pierce resistance.
as Nascarman said the best weapon for it is a Frostner or other bludgeon weapon.

Some tips that I used when I fought hime, I dug a trench between and under the "finger" pillares and put a portal under each one connected back to a base. Have a chest with extra fire resist potions near the portals in the safe area.

The portals gave me a quick egress to recover HP and stam should plus the ability to get from one side of the area to the other quickly and made it easy to do a dash and grab on my marker when i got killed.

empty you inventory of everything that you will not need. reduces the chance of not getting your stuff from a marker becasue your too heavy or the bags are filled with crap you picked up during the fight. (stone, wood, black metal scrap, etc.)

The trench also gave me some cover from Yag's meteor attack and made it harder for any adds that joined in to flank me.

Be patient and don't rush the fight, its going to take awhile regardless of the weapon.
When your HP gets low retreat, even if he has the tincy tinyst sliver of health left and FULLY recover. big mistake I always make in a boss fight is rushing back in before my HP is at cap again.

and lastly, be sure to get the best foods you can and eat them just before you start the fight, the HP/stam fade in this game ticks me off but that is how it.

Good luck.