With Phase software it is nearly as easy to correct LCC as it is to set white balance. It does not take very long because the correction is not written to the RAW files. It is only applied as a process setting, and only the output is truly corrected. So with your lenses you cannot use ACR, Lightroom, or other RAW developers to process your images because only C1 Pro can remove the Lens Casts. I have tested the P45 and A75 side by side. The P45 has more lens cast at every one of your focal lengths. My 60mm even needs correction which, with a 645 sensor, is almost a normal lens.
So while the gain adjustment with the Aptus and eMotion backs seems like a PITA, you are actually ending up with corrected RAW files. This method will allow you to process in other programs, and I would argue that the resulting RAW files are more archival and more portable. I love using ACR to process my Aptus files, and know with Phase One I would be stuck in their proprietary software in order to remove Lens Casts.
There is little news about C1 Pro V4. I have been told it will create DNG files from the P45 RAW files. These DNG files will have the LCC applied, and so they will not have Lens Cast. You would suddenly have a RAW file which can be processed in ACR, Lightroom, and others. It will also be easy to make an iView catalog and embed keywords into your DNGs. This throws a curve ball into my thinking that the eMotion and Aptus backs are creating more achival RAW files. But, what I know about Phase One, DNG, and LCC has been gotten through tech support emails and is about a product which is not coming out for two more months. As you and I have both learned in the last 6 months, it is not the greatest approach to invest in a product based on promises and assumptions. Also, the DNGs cannot be processed in C1 pro to create RGB output as far as I have been told, so you may want to keep the original RAWs if you are making DNG's.
I am familiar with your work. The Phase is definitely more efficient for you than Leaf because I believe you like shooting tethered. It is nice to have images, which are LCC corrected, appear on the computer screen when you are shooting tethered. In my test, the images from the A75-LC10 appeared noticibly faster on the screen than the P45-C1 Pro combination. Of course you know I am using a Macbook Pro similar to yours. My test was done about three weeks ago. If you were shooting a lot more un-tethered and could use an automated correction software like the eMotion solution, the current Phase solution would start to look very limiting and proprietary.
I really like the P45, but am scared because all the Phase One RAW files I have today have Lens Cast. In thirty years I will need a licensed copy of C1 Pro that runs on Apple OSXXX to process those images with a LensCastCorrection utility. My Leaf RAW files are corrected very shortly after I shoot them.