system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: The battle strategy of the inhabitants of Winterfell was ridiculous and ineffective (Spoilers)

Ok we hold the greatest strong hold in the north. Lets take our entire army OUT of the castle and line up in the open field where the sheer number of whitewalkers has a distinct advantage.

Our opening move will be to charge our calvary blindly into the dark with almost no support. They will immediately over run us forcing a retreat which will cause our infantries moral to hit all time lows. After conceding the battlefield to our enemies we will retreat behind a fire trench while dragons burn them by the thousands. This seems like it should have been the strategy from the beginning but it would have made things less dramatic. 
Our last stand will be made in the court yard where, inexplicably, a 13 yr old girl will command battle hardened veterans of many wars. She is immediately brushed aside by an undead giant by a blow that would total a tractor trailer but our paragon of feminine courage survives and manages to stick it in the eye.

Finally, in the grainy darkness of surrounding the wierwood tree, dickless traitor Theon gets defends bran stark while bran simulates a go pro drone providing exactly zero utility to his compatriots. He is killed defending the starks which does not compensate in the slightest for his betrayal of the robb stark and culminating in the red wedding. 

And when everything seems lost a girl comes out of the darkness with some flippity knife skills and explodes the entire army.
gpt
There were more people there than could fit within the walls and the Dothraki would be next to useless in the castle. As such their only potential use would be in a shock charge or a sweeping charge as the army of the dead approached. We do not actually know which tactic they used. If they did the shock charge then the Dothraki are dead and it is a major waste, but if they did a sweeping charge where they make contact then swing out to the sides it is possible a significant number survived and their sweep likely would have drawn some of the army away for a time. That is good strategy. 

The Unsullied are better in the castle defense but their most effective use was exactly how they were used. Slow the advance of the dead and allow the archers on the wall to take out as much as they could. 

The Dragons did take out the dead by the thousands, but their primary purpose was to engage the Night King Directly. Once he sent the storm they could no longer engage the ground and had to seek him out. 

Lianna Mormont was not some "inexplicable leader". She is the Lady of House Mormont, one of the vassal fiefdoms loyal to the Starks who has been leading her military for several seasons. She also did not lead the last stand, she lead her pocket of men as the castle was overrun and went after the giant that killed them. 

As for Theon's actions. That is your personal opinion. To me his actions do fully compensate for his previous misdeeds. 

As for Arya. She is the character that we have seen receive the most training of all in the entire series. She has been training to be a warrior since season one. She had magical training to be an assassin of the Faceless Men. She had been given the Valerian steel dagger used to kill the King long ago. She meets several components of the prophecy involving killing the Knight Kight King. For several seasons her kills at stealth movement where shown and in this episode when she was hiding in the library it was shown that the loudest thing in her movements was her blood dropping to the floor. So her being able to stealth past the dead and White Walkers to take said leap out of the darkness is fully explainable, as is her "flippity knife skills" and possessing a weapon capable of killing the Knight King.