but most of the ones I own in 2020 are open on the bottom. I suppose then, as well as now it allowed a variety of guns to fit the same holster.
Open bottom holsters protect the gun a little less than closed bottom ones, but they also protect the gun a little more than closed bottom ones in a different way.
While an open bottom design does not protect the muzzle from impacts as well, it does allow rain water, or anything else that gets in the holster to get out.
You may wind up with your gun in a soggy holster, but the muzzle of your pistol isn't sitting in a pool of water until you remove it from the holster.
As to some barrel sticking out the bottom, that just means the user stuck too long a barreled pistol in the holster. IT does work, meaning it will carry the pistol, but its not the intended combination of holster and gun Plus, if your pistol has any kind of largish front sight, you risk snagging it on the draw.
(Former) friend of mine borrowed my 7.5" Blackhawk. Carried it in a holster sewn on the side of a "fishing vest" It carried the gun well enough but left a couple inches of barrel sticking out. When I got back to camp and found him bitching about how he missed a deer because the gun snagged on the draw, (and saw HOW he was carrying it) I told him, do what you want with YOUR guns, I'll be having my pistol back now, thank you!
Simply put, not a good idea...