It's the gas operation, y'all
I have a Benelli M2 12-ga tactical. It's very well made, very reliable, and it kicks mercilessly with any serious tac loads. I get headaches after firing serious buck and slug loads in it. In that regard it's not much different from the 12-ga M870 I also have, except the Benelli is heavier. Both are unpleasant to shoot with all but the lightest loads.
BY comparison until recently I owned a Benelli R1 rifle with the Benelli "Argo" gas-operated system, not the inertial/recoil system of the M2. The R1 is* sweet and relatively soft to shoot, which is saying something on an 8-lb .300 Win Mag.
The difference is gas operation. Gas-operated autoloaders can indeed be much softer to shoot than fixed-breech actions; it's the nature of the beast. Recoil-operated autoloaders, not so much. That's presuming all else being equal (stock fit, pads, etc.).
I have a Weatherby SA-08 20-ga autoloader that is gas-operated. Because it's one of the lightest 20-ga guns made (5 lbs, 12 oz on the digital scales), with stout 20-ga ammo it should be a real kicker, but it's not; it's a sweetie. It's substantially softer to shoot than a venerable Remington 870 Lightweight I also have which weights a full pound more than the Weatherby. I loooove that little Weatherby
.
N.B.: I have a degenerative joint condition that over the years has made me continually more sensitive to recoil thump. But that also makes me very finely sensitive to differences in recoil effects of various weapons. When it comes to recoil, particularly on long guns, I'm sort of a canary in the coal mine.