Slingshots need experienced shooters, are better for outdoors.
Paintball markers are easier to target shoot at point- blank to 20 metre ranges.
Okay, I am not going to disagree COMPLETELY with you. In the moment when one realized the door was being broken down, and THEY were coming in, you'd grab whatever you had. If it was a speargun, I'd grab that. I'd certainly grab a shovel, knowing the huge number of WW1 soldiers that were killed fighting in the trenches with shovels, after their guns jammed or they ran out of ammo.
If there was a decorative Japanese sword set on the wall, it's going to be practice time.
And if the first thing I could grab was a paintball gun with hard nylon balls, they bad guys are going to have to deal with that.
In defense of the paintball gun, we have the fact that it projects about the same power and rate of fire regardless of the physical strength, agility, and experience of the operator. A small female or an 80 year old guy is about the same threat with a paintball gun as a 20 year old Special Forces soldier with a paintball gun.
That's not the case with the sword, speargun or shovel.
Next question is "stopping power." That's really conjecture, but it could easily be tested - just like tasers and electric shock guns can and are tested.