I asked the leader for leave, and the leader replied. It felt so strange. Shouldn't subordinates reply?

Under normal circumstances, it is true that subordinates reply "received" after receiving instructions or orders from superiors, indicating that they already know their tasks. Of course, this word is not exclusive to subordinates.

When the leader receives the instructions or task feedback you sent him, he can also reply "received", indicating that he already knows. There is nothing wrong with this, but we feel unaccustomed to it.

Including handing in homework or papers to teachers at school, teachers will also reply. So this is a very normal communication language, which can be used by both upper and lower levels.