He's just so stupidly traumatized, depressed, angry, just upset in multiple ways-
His best friend, whom he'd trusted with his everything sent him to the hospital, his best friend stole the woman vlad cherished and adored during college, they got married WITHOUT him, they had children while he can't have his own due to the one woman he'd loved so much with all of his heart get taken from him, he was left to rot in the hospital. Alone and terrified of what was going on(more than likely lost alot of sleep) and the trauma from all of this(or trauma in general) could really mess up somebody's mind in more ways than one. I know vlad was kind of stupid for putting his face directly in front of the ghost portal but not everyone thinks before they do something until it's too late— like we're all guilty of that. Especially when something is turned on without our knowledge of it BEING turned on. None of them knew it was going to just blast vlad in the face like that, I know but that's not the point.
The point is vlad had all of this done to him by jack alone(yes i know other people believe vlad is just as much to blame) but we're talking about the past, not now. Vlad is smart, he can come up with things on a whim, he can create CLONING devices ffs, has the literal intelligence to create a fully functioning hologram of maddie who literally made a jack program(im assuming cause ain't no way vlad made it) herself, etc.
But due to everything that has happened, he can't be or act like a regular person ever again. All of that at once was too much from the two people he'd trusted most and it broke him entirely. Around jack, he acts like he usually did in college. But inside, he gets hit with flashbacks that would usually trigger a panic attack but every time he sees jack, it causes rage instead.
Jack has everything vlad ever wanted yet never got. And as episodes continued, vlads usual facade was slowly fading to reveal how the accident really made him because his mind was slipping more and more until he'd snapped at jack during phantom planet. Yet instead of getting vlad any sort of help that he desperately needed, jack left him to rot in space. Where(without AGIT) he more than likely was killed by the 'Disasteroid' which, I remind you, is harmful for ghosts to touch.
Rewatching Masters of All Time (an episode i dislike for many reasons), i realized that if you just change Vlad's characterization and don't make him an abusive piece of shit of a husband, it could have been about Danny learning that Vlad could have been happy if it hadn't been for the accident and how the portal accident messed up his life in plenty of ways after seeing how Jack ended up in that alternative timeline.
So you have Danny gaining a better understanding of why Vlad ended the way he did in the real timeline while you can also have human! Vlad trying to stop Danny from changing it back because he learns what happened to him in the real timeline and he doesn't want to end up miserable that way. He has understandable reasons to be an antagonist without having to be written as ¨oh he was always evil¨ shit.
If the episode had taken this route, it could have been some good development for Danny as a follow up for TUE and probably one of the most interesting episodes in the season.
Danielle “Dani” Fenton/Phantom redesign because there’s no reason a twelve year old should show off her midriff, wear lipstick, and suddenly develop curves when transforming into her ghost form