True. But all else equal, gunshots do not attract game. Unless your in grizzly country.
I wouldn't say that gunshots attract game but I'm not so sure they really get put off by them either.
Many times at the range we have been shooting and had deer or bears walk out onto the range.
One day a mother bear and her cubs were walking across the range when we pulled up in the morning. Over several hours we shot about 1500 rounds of centerfire pistol, rifle and shotgun then walked the 100 m to a different part of the range to see the same sow and cubs chowing down on the grass, no problem.
Years ago I fired 10 rounds of 50 BMG and then had a few deer walk out of the treeline right in front of us about 150 m away.
I've also been driving to a destination for an afternoon hunt, stopped and shot a few grouse with a 20g on the way and turn the corner and run into deer and moose.
On the other hand if I was stalking an animal or still hunting in the timber for deer I'm not going to stop and shoot a grouse. I think that how much animals are spooked by gunshots differs on the circumstances of where you are, what you are after and how the animal processes information about loud noises. For instance If they hear a vehicle but can't see it they may not care about it. But if they both see and hear it they may want to move away from it.
I don't think there is any hard ands fast rule .on how animals react to gunshots, it's mostly circumstantial
But to the topic of combo guns, I've always sort of liked the idea but never seen a place for one for my hunting. If I'm on foot after large game I'm holding a rifle. On foot after grouse I have a shotgun. I keep a few slugs handy just in case but I don't expect to use them. If I'm in a vehicle weight is not a concern so I may as well have both shotgun and rifle. I could see a combo gun being useful as a tractor gun or similar I suppose. And I'm sure other people hunt in different circumstances than I do so the combo might be a top choice for them.
On backcountry hunts I have often carried subsonic rifle ammo for those days you are walking back to camp and run into some grouse you want to eat for dinner. I guess that is about as much of a "combo" that I need. I try to load them in nickel plated brass or mark them in some way so they are easy to identify.