I worked on projects on Alexa which were shoot on raw as well as Prores 4:4:4 (which Alexa) and on Professional monitors you can surely see the difference (every professional colour grader will tell you the same).
The thing about the Alexa and many people shooting in Prores with it is that in order to record RAW on Alexa you have to buy an external recorder which costs small fortune. So most of the production and rental companies go through the easy way - they just buy the camera without recorder.
Even though this is true, most of the big projects, big money commercials and films (like the one pletz mentions) shoot on Alexa are recorded in Raw, at least this is the case in my country.
So the answer is quite simple, Prores is great codec, you really dont loose so much quality filming in it, but if you have time and hardware conditions Raw is always better.