Can someone explain the ending of the sixth season to me...

Hello,

I cannot wrap my mind around two things. First, Tyrion's promotion to the Hand of the Queen's position. The way I see it, his progress as an advisor so far wasn't good. Not only he did something that the queen wouldn't be very happy about (allowed slavery for seven years), but it didn't even pay off as well as expected (the attack on Meereen happened soon). Yes, Tyrion was explaining to Deny that the attack in fact means his success (the slavers don't want Meereen to succeed), but from his tone alone it sounded like making excuses. At that point I felt that, as soon as the attack is stopped and everyone is safe, he's going to be reprimanded for his actions.
Not that I think he shouldn't be the Hand (he's the best the queen has anyway), but from how it happened it felt like he's been doing extremely well so far.
Second, Jon Snow. Here's similar to Tyrion's situation. The way I see it, his fight against Bolton was a complete failure. Bolton was clearly leading the game, Jon got into his trap, and eventually every action of his army was extremely disorganized. He led his army into a slaughter, and the day was saved by something out of his control, almost by luck. I imagine the majority of his army was lost anyway.
Yet not only he was chosen the next king of the north, but treated as some sort of a genius and superhero at that last meeting. Not that I mind him being the king. After all, he's from Stark family, and yes, he was brave at the battlefield. But still, that victory doesn't change the fact that he's completely screwed up.
Also, I don't understand how could such a victory suddenly persuade all the lords to follow him after they refused before. If they were so loyal to Starks regardless of circumstances, they would have followed him in the first place. If not, then shouldn't it take a little more than such a victory to persuade them?

Perhaps I am mistaken or failed to understand something. Maybe Tyrion's plan was in fact genius, and maybe Jon's actions during the battle were no more chaotic than any other commander's would be...