Your list got few things right but mostly focus is on wrong things.
Unholy
- Long cooldown on gargoyle is rip. Majority of DKs struggle to stay alive for their next gargoyle cd.
- CE is strong but almost hilariously difficult to land (when you compare it to any other dps ability ingame)
- Some teams require you to micromanage your targets, and abilities at the same time (eg Warlock / healer, you have to stop healing, health funnel, and kill the pet, usually solo). This becomes very easy with experience, but new DKs struggle with it. Compare to warrior, you can just target pet and it melts hue.
- Hpal teams can take a while to kill
+ Strong survivablity, vs casters. I prefer this spec in general especially vs warlocks in arena.
+ Easy to kill all non-hpal healers while retaining high survivablity.
Frost
+ High, frequent burst via Frost Strike (almost constant due how fast you can regenerate runic power most of time).
+ Hungering Cold, 10 sec aoe CC on 1 minute cooldown (very short considering how strong it is).
+ Simple gameplay mechanics (Frost Strike, Chains of Ice, Plague Strike, Death Grip, Hungering Cold ... enough to rip most of teams apart). A lot of DKs would do a lot better as Frost in arena than they do as Unholy right now.
- Squishy vs casters (ele lock, mage lock type of teams can be nightmare if you don't kill something in AMS).
- Spam dispel on Frost Fever can negate your damage outside HC / stuns.
- Dispellable snare