The classic engine and SBE are both carefully written to allow query plans to copy data straight out of the storage layer into the network buffer. 

Mathias recently noticed that Express actually does an extra copy of the record being returned here. Note that following the git blame, this was introduced under SERVER-105226, here, however, we actually did this copy before that patch landed within RecordStore::findRecord().

We should investigate why this copy is made and remove it.