It was all fine for me using Rapidash. He can be "The Guy" if you know how to use it correctly. That was also mine 'dash : Megahorm/Flare Blitz/Return/Agility
My Problem witth 'Dash was his Movepool. It was so poorly! Couldn't bother with him when i had a Infernape.
But yeah, Diamond & Pearl does lack fire types, it was sad, but not a problem