It is frustrating - I need a dark elf banner for my Kael and still can't get one and yes get way too many dwarf ones for the usefulness of dwarves overall. 

Coinidentally the only 6* kit including accessories I've ever been offered for sale is a dark elf set! 

I think it is random but i share your frustration - i need  a banner for coldheart, ran 30 spider overnight and got nothing for dark elves but got 7 shadowkin items - i dont even have a shadowkin.

The whole game is built upon rng upon rng to maximize the grindiness however so you just have to live with it. 

try different days , it seems to run like you said , 

One day mostly Skin walker stuff, the next day Mostly High Elf , the Next mostly Orc

with a mix of others in between

P.S. it also seems to run 20 Rings ,  2 necks , 1 banner( maybe ) 

I use Spider for my Advanced Quest and usually do 5 to 10 runs 5 or 6 times a week on Auto

try that and see what happens

P.S. if you are actually looking for a Specific Item , it will never drop LOL !!!

Any Barbarian item would be nice. I continue to try....   

Yeah, it's completely random. 

It would be cool if we had something like those x10 champion pulls, but like x10 specific faction accessories chance.

It would help new players who want to target specific factions only. Or with gearing the new faction :D

But the issue kind of tempers out as you get later into the game, so it maybe isn't necessary. 

Lol I always get dark elf ones XDXD

I NEED DWARF ONES PLSSSSSS

I keep getting shadowkin amulets for my 2 greens and 3 blues who never get picked to fight anything, and are bottom of the list for being ascended to be able to wear that kind of stuff.