Lol, Stannis isn't practical. Quite the opposite he is exceedingly inflexible expecting everyone to adhere to his own moral standard.
Except for that time when he pardoned all the Lords that declared for Renly. That wasn't "inflexible of him. Nor was he inflexible when Davos sent Edric Storm away, in fact, he made Davos his hand on the spot.
When he was on the council he wanted to outlaw prostitution despite the economic absurdity of it and the hypocrisy given what he gets up to with Melesandre.
Yeah, that would have been economically a poor move, but how is what he does with Mel hypocrisy? She is not a prostitute and not once has he paid for sex with her. You will note Stannis has a moral issue with prostitution, not infidelity. Get your **** straight.
He is completely unprepared to negotiate, it's his way or he will fight you.
Yeah, just like anyone with power. No one negotiates when they hold all the cards.
He is easily manipulated into believing he is Azor Ahai (which he is almost certainly not) even to the extent of conspiring to kill his brother using dark magic.
Ok, this is really where you lose it. Easily manipulated? Ummmm, if I saw a lady give birth to a shadow right in front of me, and hand me an amazing victory and 20,000 troops from nothing I would believe whatever she said. That is not being easily manipulated, that is having common sense by listening to someone with real power.
Second, dark magic? Really? Wtf is dark magic? This is not harry potter.
He knew about Joffery's (and Myrcella and Tommen's) parentage and could probably have prevented the war but instead he fled to Dragonstone.
Probably prevented the war, yeah because everyone would beleive him, especially without evidence, and without Jon arryn being around.
He likely would have sacrificed Edric Storm if Davos hadn't smuggled him away. Renly had the right of it. Stannis would make a terrible king.
Perhaps he would have, but he didn't. So yeah, you come up short here.
Also, Renly was a moron.