An asset does not have to be able to do everything, that's why we have the three services with a variety of aircraft and capabilities.
The Puma HC2 is entering service to provide a more capable platform than its predecessor in providing battlefield helicopter support in a wider variety of operating environments. If that battlefield turns out to be the littoral, that's when the grey machines of the Navy should kick in to action.
So, does Puma 2 limit RAF SH involvement? No, that's what the Navy is for (in this case).
On your first point, do you not think in these times of tight budgets and limited resources that our newly purchased platforms should be as flexible and 'multi role' as possible?
Wider variety as in 'hot and high'? Its only giving it a fairly specific increase in capability in a reasonably narrow operating area. Shame it'll miss out on the current op.
Your last point does suggest it will limit SH involvement as whatever the Puma HC 2 cant do, we'll use CHF Merlins instead.
Taking a completely independent point of view (ie as a taxpayer), do you think the cost to upgrade the Puma and its return of service is money well spent?
I'll head you off at the pass re Wildcat. My answer would be a conclusive 'No, Wildcat is not a sound investment!'