Why was Vision the weakest in Avengers Infinity War if he's the most powerful out of all the heroes?

Why was Vision the weakest in Avengers Infinity War if he's the most powerful out of all the heroes?

Basically because of that.

When it initially happened Vision mentioned how Corvus Glaive’s, well, glaive had prevented him from phasing but another effect which wasn’t directly stated but very clearly shown was that it also prevented him from repairing the damage which it had caused him. It was Wanda who had to initially seal the wound as Vision obviously wasn’t capable of doing so himself and from that point on throughout the rest of the film it was pretty clear that it was still an issue for him both with him constantly holding the area where he was stabbed and also looking in considerable pain at various points when he was seen throughout Infinity War. It was more obvious immediately following the stabbing as, even when in the Waverley train station, you could see the yellow energy fluctuating and pulsing over his body.

Although Vision is an android, his body is a mix of (synthetic) organics and inorganic materials so, for all intents and purposes, it functions as a living body. That means that the wound he received as well as his inability to heal/repair it would affect him just as a “normal” person would be affected by it and it would impair him just the same.

But I certainly wouldn’t say he was the weakest in Infinity War though. The wound he’d received from Corvus early on would, most likely, have been fatal to any of the other Avengers except, perhaps, the Hulk. After all, at the start of the film, Thanos used the glaive to execute Heimdall and where he stuck it was almost exactly where Vision was stabbed by it. Thor is stronger than Heimdall, sure, but at the end of the day, both of them are still Asgardians so if it was enough to kill Heimdall then, likely, Thor would have died from it too. So the fact that Vision was shown capable of not only not dying to the wound but also able to carry on fighting with it speaks volumes about his strength.

I suppose you could argue that he was the “weakest” in Infinity War in terms of those fighting but that was simply down to him needing to be hindered for the sake of the plot. But an argument could also be made for Bruce Banner being the weakest in it because all he done was had his arse handed to him in the opening sequence of the film as the Hulk and other than being shown to manage to take down a few Outriders he wasn’t particularly effective in the Hulkbuster armour. He killed Cull Obsidian, aye, but spent that fight having his arse handed to him as well until an opportune moment allowed him to take advantage and kill Cull.

So, with the wound Vision had I’d say an argument could be made that him fighting on as he did was one of the biggest displays of strength during Infinity War. Obviously not physical strength or usefulness in battle but, in terms of character, with pushing on through a wound that would (like I said) likely have been fatal to pretty much all other characters in the film then he showed a helluva lot of strength to do so.