In what way do you think whiteboards are like deadlines? I honestly don't understand this line of thinking.
It's not about "pressure", it's about the fact I'm an introvert and do poorly at composing while speaking. My brain requires time to focus inward to formulate complex thoughts, and interrupting any time I pause narrating doesn't give me that time to think.
I've literally never had it be an issue in my career, because deadlines happen on the order of days to months and in real life conversations it's acceptable to pause talking for 5 minutes. (Heck, in real life, it would be rude to talk the way you do during an interview, because it wouldn't give the other person a chance to share their thoughts about the problem.)