Luckily Iran has pooled together a lot of moderate Sunni tribes, to help even the numbers. In reality, Shia are a big minority. I think Manpower isn't a issue at the moment, the SAA has managed to regroup and attack on several fronts.
You're right though, 104th is no joke.
This man especially...
https://www.youtube.com/watch?v=wBRxjtgjIgg
Suheil Al Hassan has held and won against all odds, he was fighting on the front lines as a colonel for a long time, till he was finally coerced to be promoted to a Major General. He refused promotion several times, just to be able to fight on the front-lines. He reminds of Patton.