system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] why does Iron Man keep getting in melee fights if he often gets wrecked? Why do very durable characters have bad piercing durability?

That’s his standard approach for most situations against his enemies yet he ends up on the losing side. Sure he has made impressive to his suits but he still loses this melee fights or wins due to luck. Why doesn’t he use different approaches by default? For example, in Civil War, all he had to was shoot Bucky. He had bullets built into his suit as seen in Iron Man 1, 2, and Avengers 2. So why not just shoot bullets at Bucky? He shot two rockets at Bucky. 

So for the next question of the post: Characters like Thor, Kurse, Hela, and Thanos are durable tanks but are susceptible to blades. Kurse and Hela get stabbed through the whole torso by swords but that doesn’t affect them. What’s the point of stabbing them but having no effect? How do they get stabbed through torso but be ok? How, physically, can these characters be extremely durable against heat and blunt force but they’re weak against blades?
gpt
When Tony was fighting Bucky, he wasn't in his right mind, and it's not certain he was even going for a quick kill.  It's entirely probably he wanted to beat the shit out of Bucky with his own (augmented) hands, and then kill him.  Or not kill him.  Hard to say how Tony wanted that to go down.  

In other situations he does shoot from long range.  Kind of a lot.  It just doesn't always work.  

For the second part, blades are a different kind of weapon that does a different kind of damage.  You can't punch through a piece of cloth, but you can cut through one very easily.  Also a factor here is the type of blade.  We're not talking steak knives here, these are generally high-tech/magical Asgardian weapons.  They have improvements over a regular bit of sharp steel that aren't readily apparent to the naked eye.  These improvements help when used against durable opponents.