Why should it be either/or? Why should it be a classroom for children of nursery age and not a playroom with incidental learning? And what age were the children in the nursery who were running around with no purpose? How do we know thay had no purpose? Should purpose be imposed by adults?
When I ran a playgroup for 30 two and a half to nearly-five year olds, we had many activities going on at the same time. There was a sandpit, a water tank, a table with clay (not plasticene) on it, a climbing frame, a corner to dress up and play houses with table/chairs/cooker/dolls/cot, jigsaws, drawing materials, books, and a mini woodwork bench with mini real tools. Was this lacking in purpose? They were learning all the time, about the nature of different materials, size, shape, volume, imagination, working together.
The children moved from one thing to another as they wished, except for the workbench which was restricted to two at a time, by having two canvas carpenters' aprons which must be worn, and an adult stationed there at all times to supervise and make sure no-one used the hammer or saw as a weapon. This was a very popular occupation, and children would play with something nearby while keeping a lookout for a discarded apron - then move smartly in. They were learning a valuable lesson - taking turns and waiting patiently. And not braining a friend with a hammer.
At intervals we had whole-group sessions. Story time was one, elevenses was another - everyone, including the youngest, sat at tables and sang songs and nursery rhymes while the milk and snacks were brought out. They could leave the table and go back to playing, but without taking food with them. We would say "You are finished with this, then?" If they were not, they came back to the table for it. They were learning still - civilised eating habits. They did not run around. That was gently discouraged and anyone with energy to burn off was directed to climbing frame or woodwork table. Banging in nails burns off a lot of frustration. In good weather, we all went outside for part of the morning where runing around was OK.
Not all the parents went along with all this, of course. When one child (no more than a toddler) had proudly taken home a yellow scribble which he said was a duck, his mother asked me why I was not teaching him how to draw a duck properly. My reply was that he had drawn his interpretation of a duck, I could only teach him to draw my interpretation of a duck. His artistic skill would develop as he grew, but he would have been stuck with my "correct" duck..