Only problem I ever seem to have is aoe threat but even that has mostly become a non-issue solved by replacing heart strike with blood boil in my aoe rotation and the dps giving me a second to get diseases up, still can't compete with the freaking pallies though.
Spell Deflection is a weak talent and doesn't work on any kind of AoE spell damage, which is what most bosses do. You have skipped Bloody Strikes which is the reason you are having AoE threat problems, and why you can't keep up with a paladin. And you have skipped Improved Icy Touch, so I'm going to assume you have a *reliable* source of debuffing the bosses attack speed, otherwise you are simply taking more damage than you need to. Also, a few points in Scent of Blood can greatly increase your threat: you generate more RP therefore you can RS and DC more.
In terms of gear, you really want to get rid of that Onyxia trinket. Use Glyph of Indomitability, the passive armour will do a lot more to reduce incoming damage.