I will not do a tech interview

So you're basically saying that a meeting could fail to create value because an employee made mistakes in the meeting as he could not handle the stress. The correct way to solve this for everyone involved is to reduce the amount of stress everyone is under in a meeting and to create an environment conducive to problem solving. This isn't really that hard, a well motivated employee whose rewards and goals align with the company will try his best to create value as it helps him the most as well. If an employee is very bad at meetings, he could also be asked to express his ideas beforehand to someone he feels comfortable with and then that person could help him express his idea in the meeting.

The solution of hiring only people who can shout the loudest and brute force their ideas through in combative meetings is not a solution that will create value over the long term. If someone is breaking down in your meeting the problem is the meeting, not the person. Fix the meeting. Even people capable of taking stress is meetings will still perform better if that stress is removed.

EDIT: You also shouldn't be making snap judgements in a meeting that will affect the future of the company in the market. If there is a lot of tension in the meeting and the outcome is unclear, postpone the issue a short while until people can work out the issues better. If someone notices that there was a mistake in a previous meeting, work through the mistake in the next meeting and change direction ASAP. And obviously, don't fire anyone for this...

We have these differences--linguistic, cultural, even physical characteristics--that are huge. The differences that highlight a lack of shared background/experiences/origin/etc. can be found not only to be at play between, say, native and non-native speakers of a language but even separate groups within the same culture. You see that in how we handle subjective feelings of personal space, for instance --we Americans, for instance, tend to prefer greater personal space over say Scandinavian or certain East Asian cultures. But the fascinating thing is how those expectations can shift based on region, and on an even more micro level, affluence etc.

Even when the differences are minor, such as say race and skin color, the effects can be profound. If you look into what's called the cross-race effect, you'll find a tendency to have difficulty processing faces of members of other groups. If you've ever heard anyone say "all Asians look alike" or the similar "all Westerners look alike", this effect is what's behind that sentiment. And it's universal: this processing difficulty isn't limited to any particular ethnic group. Cross-racial identification statistics for eyewitnesses prove all too well just how troubling this can be even amongst ethnic groups that are otherwise readily familiar (i.e. whites identifying blacks and vice versa). But what a lot of the current literature shows is that the rate of difficulty can decrease with familiarity that shapes how we code faces and integrate them into

Anyhow, as far as communication is concerned, it's not just verbal. On the contrary, most of our cues are distinctly non-verbal: body language, gestures, expressions, prosody, paralanguage, and a lot more. People toss around Albert Mehrabian's "93%" number a lot without considering its context (namely, his work was limited to the communication of feelings and attitudes), but the broader point is that these cues serve as a means of helping to imply meaning to the words they accompany.

Now, where the really fun stuff begins is when you start to consider the universality of some of these nonverbal cues. Particularly with the face with microexpressions: involuntary expressions lasting only a tiny fraction of a second that correspond to six basic emotions. Contrary to the idea that expressions and meaning were culturally determinate, the research is fairly overwhelming that despite differences in culture, language, and even physical face characteristics, microexpressions and the emotions represented are consistent. Rules governing those emotions are be culturally specific, but how they're expressed and the emotions themselves aren't. Back in '71, Ekman went to the Papua New Guinea to show this with the Fore people even though they had almost no direct contact with the outside world up until the fifties, and at the time Ekman went, had no access to Western media or entertainment that might have given the Fore the experience with outsiders and their facial expressions.

Related to your post, however, are the findings that show we're able to recognize these expressions by people outside our own ethnic groups. In a sense, not only are the emotions and expressions universal but so too are our ability to recognize them. Biologically determined, hardwired. So talking in person, rather than on the phone, can make all the difference in the world.

If you're curious, I'd recommend taking a look at a reprint of Ekman's Unmasking the Face and Darwin and Facial Expression: A Century of Research in Review if you're curious about some of the historical origins of the work. The latter, in particular, is truly fascinating.

Confidence gives you the strength to get up and go to the interview. It tells you you're competent enough to get the job even if you freeze a couple of times.

Overconfidence tells you you can't make mistakes. It tells you you have "superior technical skills", and that freezing up is only something that happens to lesser mortals.