Manifestly not. If it were reasonable to expect this, then the founders would have written it into the Constitution, or the People would have changed the law in order to require it. The former didn't happen, and the latter hasn't happened. It may seem reasonable to you, but the whole point of democracy is that the law is not based on what seems reasonable to one person, only on what seems reasonable to the majority. And in this case, requiring judges be lawyers clearly doesn't seem reasonable to the majority, or things would be different.
This assumes that the current state of the law is tacitly approved by the majority of people, which isn't true. For example, polls strongly suggest that a strong majority (>60%) of Americans support marijuana legalization [1], but federal legalization is nowhere to be seen. Polls suggest that an even stronger majority (>80%) of Americans support background checks on all firearm purchases [2], but federal legislation again seems far away.
[1] https://apnews.com/8eb58810be2642b3a2c81e9da247ff80
[2] https://www.politifact.com/wisconsin/statements/2017/oct/03/...
No, it's not. It's perfectly reasonable in our democracy to expect judges to be trained in law in order to effectively do their jobs. Might as well let any random of the street be a doctor without training if that wasn't the case.
Non-legally trained people still participate through the jury system, and more importantly in the House where laws are created in the first place.