RMS is a real world measurement, or can be and that's why you look at it. The peak ratings that many manufacturers use is strictly a marketing gimmick to lure in new buyers who aren't educated to the fact that the peak wattage number can be any made up number they want it to be. I like to refer to the peak amplifier wattage ratings as ILS ratings, If Lighting Strikes, lol.
The RMS ratings you were referring to are measured ratings BUT they don't use music or speakers to make those measurements. They use a single frequency or tone and measure using a high power capacity resistor. It's the only way to get consistent, repeatable measurements. They have to use a single frequency to keep the output constant and consistent. They also have to use a resistor because a speaker is what's called a "reactive" load. Due to the physics involved in the inductance of the voice coil and several other physical factors the impedance, resistance or in other words the load the amplifier sees changes with frequency. So let's say at 1khz our imaginary speaker has an impedance right at 4 ohms, but say at 100hz the impedance is 10 ohms. Because of that the measured power applied to it would change just because the frequency did. A resistor is a dummy load, no matter what frequency is applied the resistance never changes. Therefore it's possible to get a consistent and repeatable measurement. Once you go and hook it up to a speaker and play music through it everything changes.
The only analogy I can come up with to explain the dynamics in music is driving on a country road. The majority of the surface is somewhat smooth and the suspension doesn't have to travel much but mixed in with that is bumps, holes and things that make your suspension travel much more. It's varying constantly and therefore is dynamic in its response. Music works much like that where the smoother parts are the quieter instruments and parts of the song (think woodwind instruments, backup singers, a rhythm guitar). The rougher parts are lead guitars, the lighter rhythm of the drums, the lead singer and the roughest parts are the hard drum beats and bass guitar riffs and those parts of the song. All together it's a cacophony of sounds in a rhythm one finds pleasant to listen to.
As far as the many more things it's a bit complicated to explain some of the aspects. The simple ones like location, aiming, mounting and deadening are easy enough and if you can get them right makes a lot of the other aspects less of an overall issue. Location doesn't mean just right where they put them from the factory. In fact the factory location and aiming are often about as bad as one can get for both. The best location depends on the speaker being used and what it's being used for. Typically the closer you can get the aiming to "on axis" or aimed at you, the listener, the better it is. Mounting refers to how the speaker is attached to the vehicle. The most common factory mounting methods are plastic rings or baffles or right to the sheet metal of the vehicle itself. Neither are great options as a speaker can produce a considerable amount of mechanical energy, especially when turned up loud. It should really be mounted to something solid, unmoving and acoustically dead. Which brings us to deadening. Deadening stops panel resonances (unwanted vibrations), mechanical noises (an interior panel slapping against the body for example), and blocks outside noises from coming through and into the cabin of the vehicle.
As you can imagine this all can be quite an undertaking to accomplish inside of a vehicle. Which is why I keep saying "as close as possible".