I'm a moderator on an internet forum that gets a fair bit of firearm discussion. As with any internet community, you get people with strong opinions who are willing to argue those opinions until they lack the breath (or in this case fingertips) to continue. One of the opinions I see come up frequently is the one eschewing various cartridges that aren't ideal.
The beauty of the concept is many different people have different concepts of ideal. They often struggle to see a perspective other than their own. And listening to a bunch of guys on an internet forum tell you how much ammo you should have, how much you should spend on guns and training, or how much gun is "enough" for a given scenario is like asking a tattoo artist how many tattoos you should get or waiting for your meth dealer to tell you when you've had enough. It's not a good idea. :-)
There are certainly optimal cartridges for different situations. If you shoot 2,000 rounds a year in handguns alone, the cost per round is a much more significant consideration than a person who shoots a couple boxes of ammo every 6 months. If you are into training, or guns, or preparedness with guns you are going to have different goals and ideas of optimal than a casual gun owner.
Optimal can be different for different people. Too often in communities or social cliques an unwritten law of conformity comes up. In the communities where people are serious about guns and shoot them a lot you'll see consensus on 9mm, 223 / 5.56 and 308. Why? Because these are all the most affordable cartridges a person can buy in their given uses.
But if people only bought calibers that were tried and true, we'd get no innovation. 9mm (9x19, aka 9mm Parabellum, aka 9mm Luger) has been around since the turn of last century. That's more than 100 years. Can it truly be the optimal cartridge for all situations? Has nothing come along that offers advantages? From a statistical standpoint, that seems unlikely. Yet it's the most purchased handgun cartridge by a large margin. (not counting rimfire ammo, which is commonly used in pistols and rifles) 45 ACP has been around just as long. When manufacturers make a lot of something it drives the cost down. When they keep making a lot of it, it keeps prices low.
The most common rifle rounds sold, 223 and 308 have both been around for more than 50 years. I find it hard to believe we haven't improved on cartridge design or the science of internal ballistics in that amount of time.
In any other industry this would be unheard of, holding on to designs for decades at a time. But manufacturers make guns chambered in the cartridges that sell, and year after year these cartridges outsell others. So manufacturers make more guns in those calibers. So people buy more of the ammo. It's a cycle that goes on and on.
Because the primary factor making these optimal is cost. I'd gladly shoot other cartridges if they cost the same amount. I rather enjoy 357 Sig and 45 GAP, but both are much more expensive to shoot. Both cartridges have certain advantages over 9mm, but the market ignores them because they cost too much, or they are viewed as a boutique round. It's the only industry that comes to mind that actually punishes innovation because it costs a little more. So we keep getting 9mm pistols.
32 H&R Magnum is a fine cartridge. It offers less recoil than a 38 Special with greater penetration and higher capacity, as you can fit 6 32 caliber cartridges in the space required by 5 38 (really .357") caliber cartridges. But it never caught on, and it's about to be lost. It's exceedingly difficult to find ammo for anymore. But I'd suggest many occasional shooters would be better served with a 32 Magnum than a 38 Special.
Similarly I've had people tell me they find the recoil impulse of 6.8 SPC more pleasant than 223 Remington. 6.8 certainly offers advantages in situations like hunting. But it hasn't caught on because the market hasn't supported it. I bet in 5 years it will be hard to find.
357 Sig offers significant velocity increases over 9mm, with a minor reduction in capacity. I find it more pleasant to shoot than 40 S&W, and would suggest real world data shows it to be a more effective round than either 9 or 40. But the market never embraced it, keeping prices high.
45 GAP offers equal performance to the century old 45 ACP in a smaller package. It seems an obvious choice. But again, it's falling by the wayside because of a lack of market support.
Every industry requires pioneers. Somebody had to buy the first fuel injected car, the first car with a turbo. People gladly paid more for those first iPhones, which revolutionized how we all use phones today. When the market supports innovation, manufacturers respond with more innovation. I'd love to see more of that in the firearm world. If everyone supported innovative cartridges and platforms, just imagine where we could be in 20 years. If we don't, we'll all still be shooting 9mm and 223. How dull.