Why did the blade stop vision from phasing

Corvus and Proxima Midnight find Vision and the Scarlet Witch are not easy prey when they attempted to take the Mind Stone from Vision, with the two battling back—and Scarlet Witch in particular doing some damage. The arrival of Captain America, Falcon, and Black Widow to help their friends would put more Avengers on Corvus’ list of enemies. The Widow likely stands out the most to Corvus, as he is injured and incapacitated by her to the point that he can no longer stand and fight.

Later, in Wakanda, more would join the struggle against the Children of Thanos, including Shuri, who attempts to stop Corvus when he once more goes after Vision. His most notable enemy turns out to be Vision, though, who ends up besting him in the end.

Family Matters

Corvus shares a tight and troubling bond with his fellow Children of Thanos—most notably Proxima Midnight, Cull Obsidian, and Ebony Maw. He never questions Thanos’ orders and often devises clever plots and ploys to defeat his enemies.

Corvus was among Thanos’ raiding party when the Asgardian ship, Statesman, was attacked and boarded. Thanos borrowed Corvus’ weapon to stab and kill Heimdall after the wounded Asgardian used the last of his power to transport an unconscious Hulk to Earth using the Bifrost.

Corvus and Proxima Midnight were paired up to retrieve the Mind Stone from Vision in Edinburgh, Scotland. Attacking Vision from behind with his spear, and stabbing him right through, Corvus downed Vision so that he could use the tip of his spear blade to remove the Mind Stone from where it was embedded in his head.

Scarlet Witch’s retaliation was too powerful though, causing Corvus and Midnight to engage in a much larger battle than anticipated. One that eventually brought in Captain America, Black Widow, and Falcon. Corvus was badly wounded in the melee by Black Widow and when he proved unable to stand and continue the fight, Proxima beamed them both back to their ship in retreat.

Using a plan where they pretended Corvus was dead, Corvus, Proxima, and Cull Obsidian led an assault on Wakanda, where Vision was being held so that the Mind Stone could be surgically removed. Even as the fighting began, Corvus didn’t make his presence known right away. Instead, he hid inside the city near Shuri’s lab, ready to strike whenever the opportunity presented itself.

Once Scarlet Witch left Vision’s side to aid her friends down in the battlefield, Corvus struck, taking down the guards and Shuri, and attempting to kill Vision when he was vulnerable. Still not at full power, Vision fought back and the two of them crashed down in a wooded area outside the lab, where Corvus once again stabbed Vision and tried to extract the Stone.

Captain America ran in to help, but Corvus was more prepared and managed to overwhelm Cap in both the strength and speed department. Right when it seemed like Cap might be done for, Vision fatally stabbed Corvus, from behind, with his own weapon.

Best reason: Because Vision is OP as hell and if he were not nerfed at the outset, how do you get the Mind Stone from him? So in short; because the writers said so. Vision's character suffers from Superman-writeritis where it's difficult to write around a hero that is damn near God-like.

However, Marvel has so many Superman characters that I'd argue that it would be rather easy to write something around Vision that shows his power, instead of having him incubate the Mind Stone until Thanos shows up to take it. I mean why not have an incredible fight with the Black Order until Glave lands a lucky strike on him? It makes more sense than a giant ship silently creeping up on them and then Glave sneak attacking an ever-aware God-droid.

But again, the issue is that Vision/God-Droid is a bit too OP for the Black Order without injury. In combination with Wanda, that fight would have been hella one-sided. Combine that with the fact that the Time Stone would also be impossible to get because the combination of Wanda, Vision and Strange is enough to prevent anyone from getting those two stones. Then bring in Thor once he gets God-level power and now the movie is pretty much over with Thanos only getting four stones.

Even Strange was nerfed at the outset, but I'd argue that he didn't even realize how OP he could be until he ran into a superior sorcerer in Ebony Maw. I think that is when he realized his full capabilities after seeing another being with like-powers be so adept. Its like when you play a sport and see someone with like-skill do something you could've always done, but you never did it only because you hadn't seen an example (i.e. crossover dribble into a fadeaway shot).

And of course Thor couldn't be OP at the outset or Thanos's quest would have ended during the opening credits. So again, Vision was nerfed because of writing and nothing more. All the talk of what the Glave can do according to the comics and stuff is all great information, but it means nothing in the context of the film, especially when you consider that he was blindsided in the most contrived manner possible. He was simply nerfed so the movie could work.