This is bad reasoning. If everyone produces less by the same amount, then even if you produce no less than the next person, the overall production has gone down.
Yes-- both general socialization with peers and social adaptation to the classroom.
Even the 12 year olds I work with who had many years of schooling have had to readapt to meet (greatly relaxed) expectations for in person instruction with several missed months. A whole bunch of 2nd graders with a wasted end of Kinder and 1st grade year is going to be chaotic.
Depression is on a big swing upwards. And there's kids in difficult situations who are not receiving help from caring teachers and social workers. There is going to be impact that lasts for a long, long time.