should helicopter time be counted towards airplane ratings/certificates of any kind?
Generally 'Yes'.
The helicopter pilot has a very healthy respect for the proximity of mother earth, has developed a high degree of coordination with the controls, hands and feet always on and is, at all times, aware that his blades are doing about Mach0.73 and what will happen if they hit anything. Hundreds of helicopter pilots have successfully transferred to fixed wing, (I'm one!).
1500 to 2000 hours of helicopter flying is, to me, far more valuable than the same time flying as P2, on long haul, in the RHS, at FL350, monitoring radios and running a fuel plot.
In the case of this accident, from the record of the captain, it is possible that he had basic competency problems, unrelated to rotary wing flying.