We are currently working on LK on 10 man and the other tank in my group is a paladin who is handling adds, while he does an admirable job tanking the adds I am struggling to keep up my tps on the LK. He hits pretty slow and does a lot of channeling when he summons adds in P1 which means Rune Strike is almost never up and this directly leads to my tps being pretty low.
I have tried switching out some gear to get more avoidance in order to get more rune strikes. However I sacrifice a lot of armour and hp in order to get there and my healers said it was a lot harder to keep me up when his plague siphon stack got high due to me sacrificing hp for more avoidance.
Have anyone else experienced this as frost tank on the LK?
I have considered respeccing blood for this fight in order to get vampiric blood and better single target tps but I feel that this shouldnt be neccessary.
The reliance on rune strike for threat is a problem for DK tanks. As I don't have rogues or hunters in my 10-man group, so I routinely struggle with threat at the beginning of certain encounters if I don't proc a rune strike before I finish my first rune cycle. Switching to Blood won't change your early TPS much. One of the best things you can do is use empowered rune weapon after your first rune cycle. That will let you perform 4 oblits during the first 8 GCDs.
You can try swapping your glyphs. Glyph of Disease is a nice glyph for simplicity of rotations, but it does nothing for your threat in a single target fight. Glyph of Icy Touch and using BS for all your blood runes would give you more threat. Since RS is a low amount of threat in this fight, swapping it to Frost Strike might be a good choice too.
In your spec, merciless combat is not a great talent for MT specs. Death Chill would be a much better choice of 1 point. A guaranteed Oblit crit on your 3rd GCD will go a long way to solidifying your threat. For the other point, I would put it in Hungering Cold. The ability has surprising utility for DK tanks. 2/3 Acclimation isn't helping your threat either. Try going 2/2 RP Mastery so you lose less RP from using ERW.