Maybe we just need more tough but unarmoured ennemies where shotguns pellets would be great. Or even just unarmoured enemies. I really like shotguns in vanilla against sections and floaters when breaching UFOs. On weaker enemies, you don't even need all the pellets to hit in order to kill, making the shotgun the most reliable weapon by far.
Also, some shotguns (military, I think and CAWS, of course) have good solid slugs that are way better than rifles close in, with good accuracy and better damage.