I'm with you on this. Loudness just doesn't do anything helpful, but unfortunately, helpful things can come with a lot of noise.
Here is something I think is helpful for finding a quieter firearm solution: The sound pressure level (SPL) is a derivative of the muzzle pressure. Muzzle pressure is usually expressed in PSI. So keep in mind, the more square inches of area at the muzzle (larger bore), the louder 1 psi will be. That's why shotguns are still loud even though they have relatively low chamber pressure and long barrels. Small bores like .22 could be quieter, but if they require greater muzzle pressure to deliver sufficient ballistics, then they may not be. Some small bores are among the loudest guns -- 5.56x45, and 327 Federal Magnum for examples. The reason for that is high muzzle pressures resulting from high chamber pressures and short barrels.
Notice that cartridges themselves are not quieter or louder. What matters are things like chamber pressure, any pressure venting out gaps (revolver), barrel length, bore size, and the burn rate and progressivity of the propellant. Don't make assumptions that 45 ACP is quieter because it's a low-pressure cartridge, or that 5.7x28 is quieter because it's a small-bore. The 45 will be very loud indeed if it is shot out of a 3" barrel and then loaded with slow and progressive powders to make up for the lack of velocity the short barrel develops. The muzzle pressure will be higher than some 357 Magnums. Don't presume that a 357 Magnum is louder than hell. If it's loaded with a very fast powder and has a long barrel, the muzzle pressure will drop to 3000 psi. A 38 Special, on the other hand, cannot be loaded to high chamber pressures by definition. Therefore, it will need slower powders to develop velocity necessary for defensive ballistics. If it also has a snubby barrel, it will be much louder than the 357 that delivers the same ballistics with higher chamber pressure and a longer barrel.
Consider that bigger bores drop pressure faster over the distance a bullet travels down the bore. Also, consider that bigger bores require heavier bullets to have the sectional density needed to achieve sufficient penetration. It's hard to get good penetration with a big bore without adding recoil. However, for any given bore size, a heavier bullet (of a given design) will achieve better penetration for a given amount of recoil than a lighter one driven to higher velocities. This is because in addition to the recoil resulting from driving the lighter bullet to higher velocities, the lighter load must also accelerate the greater mass of propellant and that mass is accelerated to a velocity averaging something like 1.8 times the velocity of the bullet. What this means for noise is that "slow and heavy," especially subsonic, will be quieter (and produce less recoil) for a given penetration goal.
Quieter guns are generally big guns with longer barrels. They need to be strong to accept high chamber pressures, they need to be bigger to throw heavier projectiles without a lot of gas and blast, and they need the barrel length to develop velocity even with a sharp drop in barrel pressure. A lot of people find that unattractive for carry. They want it short and light so they can conceal it easily and comfortably. You have to decide what your priorities are.
A silencer (or "suppressor" if you prefer) is basically a device to drop the muzzle pressure before the gas pressure front behind the bullet hits the open air. When the bullet enters the suppressor, the friction against the lands ceases but the gas is able to expand into a container with the volume of a much longer barrel. While carrying a suppressor is mostly impractical, it's not impossible. The Gemtech Aurora 2 is pretty short. This type of suppressor uses wipes and gel and the problem with that is that it is incompatible with hollowpoint bullets, the wipes only last a few shots, and you may have legal challenges lawfully possessing additional wipes for replacing them. You might consider using it with Lehigh Xtreme Defense and learning how to repack it lawfully. I'm not recommending it from any personal experience.