About the Draupnir Spear bypassing Heimdall’s foresight: there’s an instance earlier in the game when Kratos talks about being able to act without thinking in combat. Using a spear would bring that ability of Kratos to its maximum potential as “it is the first weapon a Spartan learns.”

A neat detail about Heimdall's boss fight is that once you max out his stun meter, it stays that high throughout the fight. It doesn't reset like other enemies. He's so shocked that someone landed a hit on him it has completely thrown him off his game.

I love how fatbrett was more sympathetic than odin was about heimdall's death and he thought he was an arrogant prick

“I watch your mouth move and see cities burning” is SUCH a HARD line

I love how Heimdall starts saying that Atreus is "looking to prove himself" and trying to live up to a father "he could never live up to." It has to be the most basic projection ever seen.

Something I always thought was an interesting parallel is Odin’s thoughts on both Heimdall and Thor. If you notice, Odin is always telling Thor that thinking is bad and he should just let him think for him, because he’s smarter than Thor. But then with Heimdall he says that he needs to think for himself. It’s interesting to see how Odin deliberately tries to bend both of them towards behavior that only benefits himself.

I think Heimdall being caught off guard by Kratos' making Draupnir explode is an example of what you previously stated: he's incapable of seeing the big picture.
Spear comes at him, he knocks it to the side, Kratos swings, he dodges, then the spear that he already knocked to the side explodes right beneath his feet because he's too busy reacting to the next attack to remember the big picture: the spear blows up.

The way I see it is that Heimdall has Middle Child Syndrome. He's younger than Tyr and Thor, but possibly older than Baldur so he grew up ignored and overlooked between his brothers and developed an inferiority complex as he got older. It's heavily hinted that Odin abused him and we can assume that his biological mother, Blóðughadda, one of his nine mothers and goddesses of the waves, is practically a non-entity in his life, leaving him with Freya as the closest thing he had to a mother and she ended up leaving him too. Not even a god is immune to that kind of emotional torture.

Little fun fact:
You know the moment where Kratos goes to grab Gjallarhorn after killing Heimdallr? He was supposed to grab it without issue, but in the game he sort of fumbles the first attempt, then hurriedly picks it up on the second. That was a mistake that they decided to keep in the game. It fits so well with how Kratos lost himself to his anger. He fumbles for the horn as his mind tries to recover and he realizes what he did in his rage.

One big thing about Draupnir is that Kratos mentions it was the first weapon any spartan is trained to use. The way that I saw the Heimdall boss fight is that Kratos wasn't thinking when fighting him. He was fighting purely on instinct because the weapon was so familiar to him. Heimdall even mentions after the first phase "what is going on in that empty head?". He couldn't get a read on Kratos and the ability of the spear to explode combined caught him off guard.

Notice that after Kratos kills Gulltoppur, Heimdall just says "oh well." Gulltoppur has probably been with Heimdall for his entire life and he treats his death as simply an inconvenience. He doesn't just lack empathy, he genuinely doesn't even know it's an emotion that can be felt. The tragic part is, that's not his fault. Odin never showed or taught him what empathy is. And because of that, it turned Heimdall into the psychopath that we love to hate.

The fact that he’s so shortsighted is a fantastic reversal of the mindreader trope. They usually are portrayed as being master manipulators because they know virtually everything, but since Heimdall sees so much all the time, it’s probably hard to focus anything that comes next.

Edit: I also think Heimdall’s boss fight wouldn’t benefited from the implementation of cinematic quicktime events. I felt like Garm’s fight was one of the most cinematic and fun to play and it had plenty.

13:00 Heimdall: "Gulltoppr...who loves me the most? Who loves me the most?"
At first glance this seems like a pretty normal line a pet owner might say to their pet (like "who's a good boy") but knowing the full context of Heimdall's situation of not being loved which is backed up by the fact he can see a person's true feelings and intentions (to know whether someone actually loves him or not) this line suddenly takes on a whole new meaning (as in quite literally).

From my understanding, he can read their intent and not their minds. He can predict the spear will be thrown, but not that the spear can explode.

Heimdalls's relation with Odin also perfectly illustrates what Mimir meant when he says "If he tells you snow is white, he is lying". Since Heimdall can read people's minds/intentions, he should be the first to know that Odin is a liar and rebel against him. However, it's the exact opposite, he's Odin's most loyal servant. That's because Odin's manipulation does not work by straight up lying, but rather by presenting distorted interpretations of reality in ways that always benefit him, making it look like, no matter how abominable his actions are, they are always justified. The concept of "lying by telling the truth" is really hard to explain...and Heimdall just helps us see even more how Odin is a perfect representation of it.

If watching Kratos strangle Heimdall disturbed Mimir that much, it's a good thing he never witnessed Helios' death

Something you seem to have missed is that Heimdall was sent to Helheim to retrieve the box that held the Moon on Vanaheim, which is also why he was there for the Kratos fight.

Honestly my favorite part of Heimdall is how well the writer's handle the breakdown of the arrogant bastard. He gets hit a single time and immediately becomes irritated, not scared or necessarily angry, but more frustrated. (Side note, gotta love a fight that has an organic way to introduce why a boss has become more difficult/more powerful by having Heimdall be so caught off guard that he starts manipulating time). Add on the voice acting as we approach the end of the first half and take his arm, he isn't responding like a livid individual or even a scared villain. His voice basically breaks and starts crying out that it's only luck and a fluke that he is even taking damage at all. To the end, his arrogance remains and convinces him that this cannot be happening, as if the laws of nature have come together to thwart him

I guess I would most describe Heimdall as a really powerful magnifying glass. He’s amazing at seeing tiny details and reading things, but he can never see the big picture and step back.

28:59 I'd argue that right after he kills Brok, Odin decides to just throw in that "we are square for Heimdall". He didn't even stab Brok for his son's death; he just wanted to take the mask back, and just decided to justify it as vengeance for Heimdall when it was really an afterthought. That's really how little Odin cared.