Ok....i do think we need some effort to have a good pvp set...not asking for easy mode here.
But:
1) If you have 10 pieces ( just to make my math easy) with 20% chance to find a token inside, for your last piece you will have 20% (piece chance) and 10% (missing piece chance) combined.
So, for your last piece you would have 2% chance.
2) Going deeper: If, for one bag, you need 4 victories (daily) and if you have a 33% win rate ( as republic) the final piece would make you play 4 x 3 x 50(2% chance) = 600 warzones.
Is this a korean game?