Seal of command is for trash is ICC its not a threat on boss thing they will only use that seal on trash.
The problem with your build is the lack of the real threat talents Heart of crusader, Vengance and conviction.
Your 2 points missing from judgements of the just means you are totally relying on others to provide attack speed slows and you have 5 points wasted in divinity to get 5% extra healing and 3 in stoicism to reduce stuns .. are you PVP'ing or tanking ICC????
Second time today had to provide the link .. this is full discussion on pally threat
In that discussion best threat generic live/undead build looks like
However as they discuss the there is wiggle room in the last few points in ret tree and 1 option is to move 1 one point from conviction to seal of command.
The 53 points in the prot tree are pretty standard some add an extra to fill spiritual attunement so 53/18 or 54/17 are the most common specs but very different to your 53/18 setup
** Remember Warcraft players fail in directions you never thought possible.