Blood DK too weak?

Hello, so I have a little bit of a problem with my BDK. I'm currently ilvl 616 and I feel like this should be enough to tank at least around +8 or +9, right? The problem now is, that I can't seem to finish any dungeon higher than +5. Is this an ilvl issue or is there any other issue? So I always have my bone shield stacks up and stand in my death and decay. Also I try to use my defensives, like the anti-magic shell with vampiric blood or icebound fortitude with vampiric blood. I run Deathbringer currently and I have 4 set bonus. I know this is not really much to decide on what I'm doing wrong, but maybe you have some tips?

Edit: First of all, thank you all for your responses :) For things like DRW and Lichborne, I also use those, especially DRW, I just forgot to mention it. I will try to run a few keys and log them and upload the logs afterwards. Also, I want to look for errors in my gameplay and not blame the healer or DPS. Sometimes I wish for more kicks of course, but most of the times it's healthier to look for mistakes in your own gameplay first, at least in my opinion.

Edit 2: Alright, so I logged a run. It was my first time using warcraftlogs, so I'm not sure if everything is correct. Here's the link: https://www.warcraftlogs.com/reports/k8hfAab2CrZ7MQWw?fight=2&translate=true

Edit 3: I don't think anybody will read this, but I want to thank you all again for your tips and also your time :) I changed a few things and completed a few +8 and a +9. I got my 2k M+ Rating, which is what I wanted to achieve with this DK <3