since the SH operate entirely or nearly so in support of the Army, could someone explain what is the point of having them operated by another service?
Like MGD says.
and because the core function of the RAF is air power. The RAF understands air (even when that 'air' is being used to support 'land') and prioritises it.
The Army Air Corps is not a core activity for the Army, is not understood, appreciated or prioritised by senior Army people outside the Corps, and is frequently mis-used.
Fortunately, with JFH, the strengths of the AAC and the RAF SH Force (and the Junglies) can be properly co-ordinated and well exploited.
Moreover, there will be times when helicopters may best be used in support of the RN (loading or unloading ships, perhaps) or of the RAF (moving fuel bladders, perhaps), and SH is best if tasked and controlled by a specialist organisation (eg JHF) rather than directly by Army commanders.
If it ain't broke.........