I was signed up for defense at level 25 and it wouldnt hire me... doubt it hired a lvl 12 player.
I did a siege as lvl 12 last week, it is based on the rating, not your level.
I played as attackers and killed rhalzo many times throughout the battle, fairly. Its not like he was running around dieing on purpose, is was very slow and with the little bit of lag last night anyone with 40+ ping took a disadvantage when it spiked. It was easy to run around people to hit them. (Also nearly one shot rhalzo everytime)
Rhalzo is no dueling champ (no offense rhalzo) so its not like he is going to go 40-10 at lvl 12 when he is defender and can only wear the light gear. He is a pretty decent teamfighter, but with all the armor and the unorganized spam that is defenders - it obviously hard to get in the fight, and be useful. There we also areas in the castle that displayed no flags but defenders spawned, I killed a handful of these poor souls that spawned infront of me. Rhalzo could have been placed in a similar situation.