I'm with you on that one, Yuan Benchu, these political intrigues tend to upset a force's chain of command and the effectiveness of its leaders, so it's natural that the advisors under Yuan Shao were leading causes of his loss.
Admittedly, the guy had flaws, and it seems to be his arrogance (it's too strong a word, but I can't think of anything else to substitute it with) that rendered him unable to take complete advantage of a situation (plus his indecisiveness), which didn't help when he was fighting against the might of Cao Cao.
The story of Yuan Shao is quite a sad one, since talented men get killed, fighting in vain, good advisors are dispatched and Yuan Shao's family isn't the most capable bunch of people. As for the man himself, his loss didn't come about entirely because of his mistakes and flaws. He was just in a difficult situation, and when luck didn't favour him (plus Cao Cao's strength & officers, and the confusing advice of the advisors), he couldn't surpass that which was required for a man of his status to survive. I really like Yuan Shao, he's a great character, but it's a pity he really didn't get too far.
Hungry Dynasty Warriors:
'I eat guys like you for breakfast' - Xu Zhu
'I eat people like that for lunch' - Xiahou Yuan
'Yuan Shao will swallow the North whole' - Cao Cao
'YOU DON'T UNDERSTAND! I ATE SOMEONE'S WIFE!! GAAAH!!!' - Liu Bei