So last night, I decided to get the Glass Bow of the Stag Prince on my Ranger. Then, wandering around the Rift, I found Forelhost. So, I went in, health potions aplenty, and I'm being devastated a few rooms before Rahgot. I had this same problem with the main questline of Dragonborn, where Seekers forced me to chug health potions. My health is capped at 200, and I have a fast healing spell.

So, I'm still being pbliterated by Draugr Scourges, Draugr Deathlords, Draugr Death Overlords, etc. I can't kill them with my bows when they Unrelenting Force me constantly, and my daggers are weak, so I've only been able to kill them through Onmund, and some well-placed shouts near traps. So there is no chance of me killing Rahgot with a glass dagger of fire in one hand and a healing spell in the other, so how would a ranger go about doing this? Also, I haven't upgraded any magicka.

stand far away from Rahgot and use your bow so you have enough time to dodge his magic.

This isn't really helpful for this situation but I'd like to mention poisons! Always gotta have those poisons.

Try and have your first shot be a sneak attack, like michael said try staying as far away as possible, take cover, do you have any way you can stagger him?

Lol, Forelhost is notoriously hard. Last time I went through Rahgot and his friends chased me like halfway back through the dungeon. Luckily for me ther was a spot where Rahgot got stuck and couldn't advance and further and didn't have a complete view of me so he wasn't casting so he just stood there for like 5 min until I pot shotted him to death. Pretty cheap on my part but I wanted to be done with it.

One of my very favorite dungeons. Sneak. Sneak. Find them before they find you. Go slow and use sneak, muffle, invisibility. Use the area for cover. I go as a sneaky sorceress and have few problems. I do hate to say this, but get you a better bow. The glass bow of the Stag Prince is mostly for animals. Get you an Ebony Bow or a Dragonbone bow and improve them. Use arrows to match the bow. Make sure you have the Deadly Aim perk in the sneak tree as it makes bows do 3x as much damage in sneak mode.

take a bow and return later

Another thing you can do is if you have a scroll of circle of protection or gaurdain circle you can cast it on the doorway and most hopefully only Rahgot will be high enough level to pass through it so you can fight him alone instead of him and all his buddies at the same time.

Kill Rahgot and the rest will go down cause the boss dies.

It's possible to aggro the deathlords, deal with them first and then take on Rahgot. Your advantage here is that the room remains open, so you can backtrack far enough to lure them where you can take on them one at a time.

Okay, so here's my second attempt. Got my 70-something damage crossbow on Onmund and I, ebony war axe and sword, Onmund in full ebony, and a bunch of healing potions.

Okay, Rahgot's dead.

Good job.