Yes, I personally prefer the look of Alexa's images to anything else out there digitally at the moment. But there are times when the more contrasty and resolute image Epic provides is what I need, and there are times when the clarity and naturalism of Sony Cinealtas are what I want. These sensors are our filmstocks these days, and I for one, would prefer we keep a little variety.
Your post makes perfect sense Mark. Paradoxically, given what you say, you should fully support the Dragon Interchangeable OLPF system, instead of asking yourself why you need it!
To achieve different looks, do you want to rent an Alexa, a Dragon, a Sony in each particular case? I bet you don't.
With RED's system, you would be able to achieve these "different film stocks" looks by simply swapping a $200 OLPF instead of renting/buying different cameras.
I am ALL for a film-like (or Alexa-like) OLPF for the EXACT reasons you mention in your post.
Happy Holidays!