Now I can certainly fire indiscriminate unaimed shots faster with a semi auto but that does not make it more deadly by any means.
In a crowd of people it does because aiming is not involved. For hunting game not so much.
Here is a clear example of firearm and hunting ignorance. A crowd is a crowd, whether geese, buffalo or people. Apples and apples.
Aiming
must be involved if one expects to hit the target with effect. When shots are fired a crowd will naturally scatter in all directions before the instinct or thought process to flee in one general direction of perceived safety kicks in. Geese, ducks, buffalo and people all react in a similar manner when the crowd is threatened. At first, there is a general confusion and milieu. It takes time to gather into the 'flock' or 'herd' mentality and flee as a crowd. Even then, there is much more space between objects than you would imagine.
In order to be successful a predator must focus on one single target. The same holds true for a 2 legged predator. A goose hunter or an old-time buffalo hunter must pick out a specific target and fire for effect at a critical body point. Anything else is ineffective and risks merely wounding. Merely blasting away at a mass will give poor results. Most shots would miss anything at all. The few that hit are much less likely to hit vulnerable central nervous system points. The reason people die in mass shootings is
because the shots are aimed at critical body points.
If it were all 'spray and pray' as you suggest, the death rate would be much lower and the survivable wound rate much higher. In most mass shootings, the victims
were not all gathered at an exit, but they were scattered through out the target area. Aimed shooting. The last time I went goose hunting I fired 4 shotgun rounds. I killed 3 geese. (I keep 1 round between the fingers of my off hand for a quick follow-up load) Aimed shooting.