There’s that, but there is also the situation where lawyers know the law, while ordinary people don’t. But ordinary people can decide facts without trying to apply law to them.
All a jury does is decide the facts, and nothing else. Then the judge interprets the facts in accordance with the law. The problem with having lawyers in the jury is that a lawyer on the jury will often try to apply the law to the facts before the judge gets the chance to do so. Thus your “kind of authorative” comment; a lawyer in the jury will want to apply law to the facts, thus acting as a de facto judge before the verdict gets to the actual judge.
It’s the “if the only tool you have is a hammer, every problem looks like a nail” situation. Lawyers know the law, and their natural instinct is to apply the law to every fact. I should know; IAAL; and while I cannot speak for all lawyers, I cannot stop at the facts. I have to go further into the law that obtains from those facts.
That’s why lawyers cannot serve on juries in Canada. We have too much legal education, and we’re too willing to use it where we shouldn’t. Like on juries.