Walt leaving the Whitman book on the toilet
Hubris. Walt became so comfortable in his life as Heisenberg after Gus's death that he overlooked such a simple detail. Yes, it's a stupid thing to do, but it's a stupid thing the character WOULD do, which he even admits to Skyler.
burying ALL SEVEN barrels in the same place,
Seriously?
falling for the fake can/phone call thing and driving out himself instead of just telling Jesse that know that he knows where he is he'll be sending a crew out to kill him and everyone he knows if he burns one dollar
He fell for it because of his greed. Just like Hank says, the dirt didn't match in the photo, but he knew Walt would be seeing far too much green to catch something like that. Think about it, this was EVERYTHING Walt had worked for. When he thought all of that was about to be burned to ashes, instinct and greed took over.
failing to realize Hank had to die, offering all his money to save Hank, etc.
What was he supposed to do? Just let them kill him without question? If Hank died, Walt knew that this would be the point of no return. Once this business hit his family, that would be it. Walt knew that, and he tried to do ANYTHING to prevent it.
Jesse suddenly having a Ebeneezer Scrooge personality shift
What? What does that even mean? That he was grumpy? He wasn't grumpy, he was depressed and wrought with guilt over Drew Sharpe, Gale, having 5 million in blood money, etc.
teaming up with the cop who beat him up with no hard feelings at all
Did you even watch the episodes? Jesse refused to work with Hank for that very reason, but when he found out Walt poisoned Brock, all bets were off.
and then basically being his ***** when Hank has no real power over him
Sure. Which is exactly why Jesse didn't go through with Hank's plan to bug Walter and instead opted to take him down with his own plan
going out to the middle of the desert with no gun and only two DEA agents.
Gomez was the only one Hank could tell until he had enough evidence to bring Walt down. And if you're saying that he could have brought in the DEA once Walt confessed on the phone, that wouldn't work. They need Walt's money as physical evidence, and he wasn't going to hang around waiting for them while they explained the situation to the rest of the DEA.