Not for locks. While having mana is important, sta is a great stat to have - your pet gets part of that and you can Life Tap for mana. Plus, that lock is Demonology specced and heavily into pvping in the arenas. The key about the arena is take your opponents out before they do you.
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
Yep. Having Stamina is great, even at my level im holding off against level 39 Warrior twinks with Epics. Im going 42 Afflic and 14 Demonology for the extra health and such:
Demonic Embrace: 5/5
Imp Imp (lol): 3/3 - for instancing and teh extra Stam!
Imp Healthstone: 2/2