How do we theme node view component?
Your hook_node_view() is incorrect, check the documentation and example implementations. The first argument is a $build array. That's the new $node-&gt;content: What your code is adding to $node-&gt;content should be added to $build.

Also, never render things yourself: Just put your render array ($node_statistics) in $build['content_statistics_list'].

It's also recommended to implement hook_entity_extra_field_info() and expose that key as an extra field. Then it can be shown/hidden based on the view mode.