^ they're not really designed to be used in job interviews; their use in that context (though moderately common) is pretty random. They are useful for improving how an existing team works, though. Personality testing is very informative indeed, once you interpret the results on their own merit. To say they're worthless is pretty inaccurate; they actually tell you a lot about people, though not in a way that's particularly helpful to a job interview.
One thing that I think needs to be cleared up a bit is the definition of introversion, because some people seem to be equating it with being shy. Introversion and shyness are two independent things.
Thank you for posting this already; it's what I was itching to post while reading the thread.
However, the conclusion I would draw is a bit different.
Being an introvert in itself is not a valid reason for not being an engaging and vibrant person to be around. Almost any introvert, with practice and training (sometimes a lot of it!), can do it. They can even enjoy it, or learn to. They'll just be exhausted by it after a relatively short space of time, compared to an extrovert.
In fact,
because introverts often apply practice/training to people skills, they can end up being
better at it than extroverts. Untrained extroverts can be unfocused and random in their interactions; whereas a practised introvert may well be more effective, because they've honed the art of balancing listening and talking.
Introverts may well also be shy, but there are also shy extroverts, as you say. Overcoming shyness an important first step to improving people skills in either case. The next step then varies; the introvert needs to learn to tune into interpersonal interactions in a somewhat different way to the extrovert.
Introverts will notice the interactions and interpret them as being a function of themself, and they need to learn to parse out what is them, and what is other. Extroverts will automatically tend to assume the interactions themselves have a life of their own, and "forget" that individuals, often with conflicting agenda, are driving those interactions forward.