Why navies still need the rank of captain

Would removing the rank of captain from a military organisation have any benefit?

No. Ship command is a specialised field, and the captain rank clearly expresses a distinct naval command path.

A captain may be a role aboard ship, but it is also a useful rank that expresses a distinct professional command path. Running a warship demands specialised experience in ship handling, combat systems, and the organisation of a crew at sea. Those skills differ from commanding an infantry battalion or an air wing even though all three jobs require leadership. Attempts to flatten the titles within unified defence structures repeatedly recreate specialised branches in practice. The panel therefore sees removing the rank as a useful fictional plot device but a poor model for a functioning navy.