You deeply misunderstand what I said.
You asked and I told you.
I will tell you again so you understand clearly ,your DK's will get buried in PVP without a dedicated healer,I know I ran a 5 man team from the day WoTLK launched and struggled through Arenas and BG's until after months of PvP,I got sick of being CC and burned down.
It doesn't matter how much plate you have,once the op4 get wind you are boxing DK's you will get CC'd,and AoE'd down.
But like anything your experiences may differ from mine and I wish you luck.