Let me be clear, I'm not criticising Parker's form this year. He was tireless, worked hard, was inspirational at times, he deserved his player of the year award for his sheer consistency and contribution to the team.
BUT, I don't think he offers us much as a lock forward. He's more a workhorse second rower. I'd rather have someone who makes a few less tackles and actually has an impact in attack and defence, rather than him who tackles (often 2nd in) all game and makes some hit ups without often threatening the defensive line.
But there's only so many forwards you can pick, and his size counts against him being anywhere but the back of the scrum.