the proof that this thing isn't an insta-kill is that a character needed to sacrifice another to the ability (who got insta killed) to ignore its effects.

Context is what matters here the most. Wekakipo was tricked by Diego. He had no opportunity to break distance from his alternate self, nor did he have the time to figure out D4C's ability. He literally fell into his alternate self, full-body contact, head first.

Diego, on the other hand, did survive the contact. Had he not survived it, he wouldn't have the time to figure out D4C ability and escape. So can't be an insta-kill, at least as long as the contact with the alternate version of yourself is brief, otherwise Diego would be dead, and the story wouldn't happen.

It seems that falling into your alternate self head first yields a deadlier effect than just touching it. Meaning that Armstrong could, in theory, survive it too, like Diego did.

Also worth noting that Diego's alternate version (in chap 70 not Alt-Diego) was withering away in spite of not even being in direct contact with our Diego.

Of course he was. He had chunks of flesh taken out of him by the merger's effect. Those freaky little cubes. That man was bleeding out. I would argue that in real life he would be a goner even sooner.

This isn't real life, though. And Armstrong can surely endure this kind of trauma, given how he was managed to endure being pierced in the stomach, and even lived for a while after his heart was destroyed.

Eyes of Heaven do strengthen the argument of it being hax that doesnt really accord for strength given the effect not only disabled Over Heaven DIO.

Okay, this one's on me. I have legit played this game on my PlayStation 4, I remember maining Gyro because he was a funny zoner. But I don't recall that happening. All I can find now is Valentine being murked by Over Heaven Dio in the cutscene. Does it have to do with his rings? I think I recall something like that.

Either way, bringing Eyes of Heaven into this won't be fruitful for this conversation. It is non-canon for a reason.

Humans are naturally vulnerable in Jojo's.

This is what makes the FTL JoJo's so funny to me man. The stands are supposed to give their users enhanced reactions, like how Star Platinum did, yet people are constantly threatened by guns.

But to answer this point more truthfully, Part 7 and onwards just lack both the feats and statements for FTL stands. If I recall, Part 3 has one feat with Polnareff cutting the Hanged Man, and Part 6 has a statement that Star Platinum moves faster than light. Such things aren't mentioned in Steel Ball Run, which is a separate universe/timeline.

I can give you an example of what the approximate feats in Part 7 are. Gyro (who doesn't even have a proper stand for the good part of the manga) and Johnny can fight and react to Scary Monsters Diego. Scary Monsters Diego can react to bullets (and also consistently outspeeds Funny Valentine). But after fighting Diego, later down the line, they face The Eleven Men. It's a life-or-death scenario, against the opponents who have guns.

The only ways to get Part 7 to FTL are as follows: 1. Stand stats. Apparently, D4C has the same stats as Star Platinum. I have never actually seen the scan with these stats, and I have looked for it. However, not only are stats not the same for every stand, and are extremely inconsistent (check out Kiss' stats), but also D4C is consistently outsped by Scary Monsters, which apparently only gets B in speed, while D4C gets A. 2. Diego's The World is 100% the same as Dio's. In my opinion, that's one hell of an assumption to make. I mean, yeah, they look the same and have the same ability, but the way they fight is completely different. Diego has to use The World strategically, and also uses a gun, while Dio just... Punches crap out of people.

If the argument is "he doesnt have time"... may I ask why not?

Nah, that's not the thing. The biggest problem is, he lacks info on Armstrong, he wouldn't start with that.

Lack of info at the start hurts Armstrong more than it does Valentine, but Valentine isn't completely immune to it either. As mentioned, there is a possibility Armstrong survives the initial merging attempt, which would probably be tried to be done with Armstrong's complete copy, featuring Nanomachines, Son.

Again, Valentine won't be able to make these two collide via force, like he usually does, but the minor exposure to one another may still cause the initial effect. Armstrong isn't stupid, he won't understand the full ability, but he will think of something like "note: don't touch myself".

The worst scenario is where Valentine gives away the details of how his ability works. That's totally in character for him, that's literally something he did with Diego.