Beyond frustrated at this point

So maybe everyone here can help calm me down a bit. I have been playing wow since release with RL friends I have known since high school (about 11 of us in total). We all keep in touch by playing almost everyday throughout the years and we have had many funny and memorable experiences. I know this sounds great (and it is) but I have started to loose interest due to this messed up legendary system.

I have around 15 days played at 110. I have most time played out of all my friends that I play with. I was the first in our group to 110 and did everything I can to teach everyone about the dungeons and boss mechanics from normals to mythic and now to mythic+ and even EN. But the thing that has been getting me down is the fact that EVERYONE in our group has a legendary except for me. I know this seems like a qq post and it probably is but I don't know what to do anymore. I feel like in just dragging everyone down in terms of damage now. I am pretty low in single target dps and I am not putting out the damage that everyone else is during raids or mythic+.

I know my spec well and have been playing Death Knight since Wrath. I absolutely love playing my DK more than any other class I have leveled but due to bad RNG I'm falling behind everyone and I just feel like a hindrance towards mythic+ progression.

I have done every emissary mission since I hit 110, I run mythics and mythic+ constantly, I do my daily heroic or 2, and clear EN weekly. It just sucks to feel that I cant progress anymore without a legendary and my class is one of the worst of the expansion.

tl;dr Feels bad man...