I always see this argument that ppRGB is too big. Maybe there is a misunderstanding of the process of moving from a working space to an output space in thinking that the entire working space is mapped into the output space so using a space as big as prophotoRGB is problematic. At least that’s the only possible “theory” I can come up with as to why it would be a problem.
But ppRGB is simply a container that is large enough to contain pretty much any color. This means moving from ppRGB to an output space will move whatever colors in the image into the output space, using one of two logics ... move any colors necessary to try and maintain the relationship between colors (perceptual) or try and leave most of the colors alone and clip out of gamut to nearest color (relative). It doesn’t matter if the working space is way larger than necessary, the empty space outside the image gamut doesn’t come into play. I’m not sure why clipping into adobeRGB would be advantageous instead of moving to the output space.
In the case of the OP, the idea of first clipping to AdobeRGB, then moving to the final output space seems counter intuitive, because blues are where the Epson printer has an advantage over AdobeRGB.
I haven’t used AdobeRGB for a long time -several years ago when my 9900 printer arrived found many landscape images with blue sky suffered if I used AdobeRGB as my working space I have found issues where I didn’t take the time to soft proof, even if it was for nothing more than deciding which rendering intent is better suited for the image, and yes there is the occasional image which requires some tweaking to get good results, but clipping to adobeRGB first, while perhaps solving the problem, has never yielded a better result.
I have seen issues with some very specific shades of blue ( in this case based on the preview the blues appear to have easily become synthetic in post processing, thus contain colors outside of the cameras original colors, adobeRGB and the printer gamut). I wouldn’t be surprised to see this file take some effort.
And I would agree, some extreme synthetic blues a canon printer can pull off easier than an epson.