See, I read that more as he's a soldier. Moreover he's a general. This is what he's good at. He saw the attack with the wildfire for what it was. He knew they'd shot their wad. He regrouped and he led the attack. He didn't cower like Joffrey. He didn't hang back. He charged. And I thought his being held back was more because he was in the moment. He was in his element and he is not the kind of guy to back down. Ever.
I like Stannis. I have since his very first scene with composing the letter, which was just hilarious. He's got a ton of problems and character flaws, but he's one of my favorite characters.
He has middle child syndrome. He watched his brother grow fat and lazy and probably had problems with how he was letting the country to go to pot, but I think if he thought Cersei's children were Robert's, he wouldn't have done anything. And if Renly were older, I think he would have supported his brother. But he knows the kids are bastards and he, not Renly is the older brother. Therefore, the way he sees the world, the throne should be his. But time will tell....