In such an important technical/mathematical discussion, one expects accurate information & statements, not sloppy BS.
He failed in this respect, and this upsets me with such people. They are not serious, they just disturb any serious discussion with their insistence on their wrong thinkings. And when asked, they won't nor can't prove their claim, instead go to insulting & badmouthing mode...
I'm investing precious time in such discussions, to learn as well to inform others. I'm not interested to discuss with such idiots who can't follow basic etiquette.
Mathematical and technical discussion??!! Really?? You haven't reached that level in options trading yet tbh that I would need to involve mathematical and technical discussion when you can't even look at a PnL diagram to see where the potential risks of vertical spreads are.
And prove to you?? Seriously??!! It's your trading and your life? What is it that I need to prove to you for?? LOL I already did you a favour by telling you vertical spreads are riskier than you think and showed you where and how you can evaluate the risk. I still need to prove to you??!! LOL The time when you lose everything that you have earned will be my proof.
I don't wish losses upon people but to people like you, that's the only way you will learn. LOL Good luck!!
Still, above I alread gave the answer, at least an important hint...