I average 300-400 rounds per week of 12g and I don't have the same feelings about that. A properly fitted 0/U held tightly against the body is not significantly more difficult to manage than a semi, and offers several advantages. Most people who experience pain from shooting are just not holding the gun tightly in toward the shoulder. Only when it's held loosely, with the hope of avoiding impact, does the gun kick hard. The tighter you hold it, the less punch or kick you get, it only feels like a flat-handed push. Those who lean back on the swing instead of leaning into the gun, also find it painful.
I own and shoot and teach clay shooting with both types of guns, because it takes several size guns to fit all the potential students, but I find myself using my high-quality semis for my own shooting very rarely.
Expanding it to a safety issue, I much prefer to be standing in a group of clay shooters with O/Us, because I can easily tell when a gun is really truly safe.