In the real world, Stannis would have had much better armor, fortification of the gate would be much better, they'd be dropping hot tar and fire over the walls onto everybody, Hound wouldn't have taken his attack party out of the gates, and Stannis' first ladder would have for sure gotten knocked down

The budget is a huge, huge deal for many of the battle problems. But FWIW, I think they did it pretty well. Only a handful of large battles on screen have ever been good. I was dreading the battle scene since the first episode because almost nobody does them well. GoT has been up to HBO standards though. It's not on the level of what Spielberg and Scott can make, but it was very good considering that TV fails at all things fighting/battling

As for why Stannis did what he did, it's well within reason that he believes in himself like that. Like when Davos told his son to "not tell Stannis he's not a god". Even though Stannis' actions are largely silly, it's okay because that's his character. He's the world's most stalwart badass despite the fact that the main reason he's not dead is luck. If he wants to go up the ladder first, he's doing it; and his decision to do so have little to do with how safe and smart it is