For me when you get to post and you start messing with the files you realize why larger productions opt for an Alexa/RED.
We have options now like the Raptor that only weigh 4 pounds and can be powered off a small v mount battery. I would say the Raptor dynamic range is very similar to the S35 Alexas. What it delivers over them is that it holds the dynamic range in the shadows. At 800 iso the Raptor is much cleaner than an Alexa mini, but with much less highlight retention. You can boost it to 2000 iso maybe even 3200 iso and still get a nice image. The Raptor pictured below could be rigged even smaller (smaller monitor, smaller lens, no top handle). There isn't much you can do to get an Alexa smaller though. Even the mini is 8 pounds with just the body and viewfinder and is also a powerhog. The Alexa 35 is even larger.
I did a feature a couple weeks ago on the Raptor. As convenient as it is to use I think we would have been better off with an FX3. The crew was so small that any convenience is a big deal. This was our rig, I traded size for battery life.
All this to say I really do notice a difference shooting with Alexa/RED
But after putting the files to a REC709 colorspace and adding a lot of contrast which is what I usually end up doing, the results between that and a mirrorless can definately be hard to tell if it was shot resonably well. The truth is you can sometimes shoot things better with a mirrorless. It saves you time, which then gives you more time to fine tune the things that actually matter (lighting, composition, etc...)