I don't think Apple prioritize RAWs that much.
Their API for saving to the Photos app works well with standardized files such as JPEGs and PNGs, but all the different RAW formats sometimes make it trip up.
If you want your RAWs untouched you could buy ShutterSnitch
- that'll receive from Eye-Fi cards and from there you open the files in editors that support the "Open in" feature of iOS. (Which PhotoRaw does)