A better comparison would have been to the Red Scarlet-W. For about the same price, you get 5K, a proper RAW format, and excellent image quality.
Also, the Alexa sensors were quite amazing considering they're 7 years old now, but it would be pretty boring if everything had the "Alexa look"
The point of my original comment is that whether it's an Alexa, an A7s, or 35mm film, HDR acquisition has been here for a long time and Arri isn't in a league of their own.
It's all about creative choice. The Alexa has nice highlight rolloff and great color, no doubt. Red Helium has very clean shadows. Alex is measuring about 14.5 stops on a DSC Xyla 21. The Red at least as much (http://www.reduser.net/forum/showthread.php?149166-Weapon-cf-vs-Helium-X...). The technicalities miss the point. It's about the look and what you can do with it.
So what do you want to do creatively? David Fincher loves the Red, and others swear by the Alexa, Nolan and Pfister are loyal to film. For me, I've shot on Red, Alexa, Sony, etc. For me it all depends on the project. Heck, I'd love to do a project on 16mm. Black Swan looks great.
Until someone comes out with a camera that has 20+ stops with clean high ISO and great highlight rolloff, we have tons of great options out there, and the all can produce amazing HDR.
In that way it's exciting times. You can't blame the camera, regardless of which you choose. Arri's marketing video is a testament to the amazing talent of the photographers, rather than that their tech is better than film or Red or whatever.
You're exactly right. We have great tools to work with. Cameras have become so capable that they're becoming the new "film stock." You can now choose what fits your creative direction. Max Mad used nearly every camera out there from BMCC to Alexas. Deakins used A7s's for nightvision in Sicario. Wonderful that you can have 400k ISO and 13.5 stops on a mirrorless camera. So I am very happy that we live with so many incredible options to enable our creativity
My dream scenario would be Alexa color science with a Red sensor (and Red price). Then you have that wonderful creamy look that we love plus enough resolution to finish in 4K and all of the niceties that come with having extra pixels in post.
If Alexa latitude was in a class of itself it wouldn't need marketing. Alexa sensor has about 14 stops of latitude, not too different from Kodak Vision 3 35mm film. Red Dragon and Helium sensors are beyond that. Any of them are plenty good for HDR. Alexa's main selling points are the Arri ecosystem of products, its now broad usage from acquisition through post, and its extremely good color science. Latitude isn't what makes it stand out
This kind of marketing fluff really annoys me. 35mm film captures "HDR" as can any camera that can do 10-bit or higher raw/log with a decent dynamic range. HDR really amounts to higher luminosity, wider color gamut/bit-depth, and new transfer functions. Film and digital sensors with good latitude and raw or good log codec will generally exceed these requirements (and have for a long time). HDR is much more about post and display, than acquisition. Consequently, Alexa isn't special when it comes to HDR.
Despite the marketing it's not about gear, it's about how to better tell your story when unshackled from the creative bounds of SDR's lower brightness and smaller color gamut/bit depth.