In many cold parts of the country, snow falls and stays fairly consistent in its texture for a long time. For example, the high/cold parts of the Rocky Mountains. In that environment, if you know how to wax a waxable ski just right, you can get superior results. Unfortunately, I operate in California, and it is possible for the snow to fall and stay powdery/sugary for a while, but more typically it starts to transition within hours of the first day. A California ski tourer ends up going through four kinds of snow just before lunch time, and it is impractical to keep changing wax for that. So, waxless skis are practical for California snow, mostly for convenience. They aren't perfect for anything, but they are the practical solution of choice if you operate in a changeable snow environment.
Metal edges on skis come in several forms. One is a solid metal edge. One is a cracked metal edge where short segments interlock together. One is a partial metal edge. A solid edge is the most durable, but a cracked edge is more flexible and hence easier for carving a turn. Even if you are not a serious "turner," a metal edge ski is much more durable than an ordinary plastic edge ski. So, if you tour in the backcountry, it is a safety feature that may allow you to return in one piece. Metal edges do add more weight, but I think they add peace of mind.