The things that I think truly defines a pistol as worthy for "combat" are a little more precise due to my experiences. From what I have experienced, pistols in a holster do not see much of any aggressive fouling from the environment until it is out and being used. With that, I see the need for a pistol to function when submerged in quicksand to be highly irrelevant. Though I do believe that the ability to function with reasonable amounts of foreign debris is quite a relevant consideration. That said, I will usually refer to pistols that have a long track record in high conflict such as ours. Also I will refer to countries that use their pistols in many different environments. This is very important and I feel that people misunderstand just how reliable some pistols really are.
Another consideration to take into account is certain aspects of the pistol such as service life, being employed with gloves, the trigger characteristics, the sights, and even down to the setup of the controls and size to capacity ratio. Let me break these individual subjects down for you in more detail.
The next priority on my list is for the pistol to have a long service life with all stock parts. This automatically disqualified the Glock from my consideration. If you have ever shot a Glock like you would if you were to fight with it, you may find that it was not designed to have long lasting parts. The focus is on customization and easy change of parts. I prefer though to not have to replace parts so quickly. There are many pistols with long lives on their frames and barrels, but slides and springs tend to get neglected often these days. The companies that I find that are considerate of these issues are the Koreans, and the Germans. The H&K pistols seem to have proven to have a long service life with the German military. Walther also has proven to have a long service life as well. The German police have been seriously pleased with the performance and long lasting characteristics of the pistol, hence why it remains in service. The LH9, being a modernized version of the DP-51, inherits all of the reliable characteristics of the DP-51 that make it a formidable pistol when looking to satisfy a long service life. The springs of your fighting pistol should be heavy, guaranteeing a long service life. I believe that the life of springs are of the utmost importance when considering a pistol, because one spring breaking can shut down your pistol all together. That being said, let us move on to other considerations.
I am a huge advocate of the use of gloves, and that means that my fighting pistol should be easily used with gloves on. This variable can save or defeat a pistol from my service. This segways us into a discussion of grips. The pistol needs to be able to be used with gloves on, and that includes a comfortable grip and trigger reach, allowing for a natural point of aim and easy manipulation of the trigger, no matter what type.
With the consideration of trigger manipulation with gloves, we also must face the fact that we tend to not be affected by the weight of the trigger as much as we would be barehanded. I find that gloves not only damped the sensitivity to the trigger weight, but also on the affects of recoil. This plays a huge part in how we perform with followup shots. I find that as far as trigger characteristics, the heavier trigger on double action and on striker fired triggers help perform more accurately out of the holster.
Without the help of sights, our ability to make accurate hits like head shots are severely inhibited. Some advocate that sights are not really needed in order to hit your target accurately. But most of this is advocated by people with little to no experience in all aspects of engaging someone with a pistol. This does not make them wrong, but it sure does raise questions on what makes them think that they can establish standards for others blindly and universally.
Sights are designed to give the user the ability to hit precisely and accurately at range. I will agree that at close range, sights are of dubious value, though. But when making a precise shot when you don't have access to a rifle or have only a pistol at your disposal, you need to realize that learning to aim your pistol properly is of utmost importance. The sights therefore must be strong, and allow you to cycle the slide one handed. Many dismiss this task as being unnecessary, but I find it to be a fundamental requirement.
When considering the controls that a firearm houses, it is important to realize that we need to look at them for what they are designed for. A decocker that is reachable is a shooting grip is of dubious value when you consider that the point of the decocker is to deactivate the ready position of the trigger. Also it is important to consider the fact that these controls should not get in the way when using a full firing grip with gloves. When we talk about safeties, we need to realize that the safety is an integral part of the pistol and should be treated as such. In a 1911 manual of arms, you will find that it is vital to put it on safe when not shooting and to rest your thumb on that safety when shooting the pistol. Thus, it is important to use the safety on the pistol you are "fighting" with. That said, if you do not wish to have a safety on your pistol, you must decide if there is a model without one, or if it is a deal breaker totally.
The size of the pistol can have a good amount to do with the effectiveness one experiences. Traditionally it has been known that the bigger and heavier the pistol is, the less the recoil and the more accurate it is and the easier it is to shoot. Lately this is the being found to not only be untrue, but also unnecessary to follow as a guideline when considering a pistol to be put in the category of "fighting" pistol.
In the sense of capacity, it is important to note that your only concern should be the fact that the pistols' size matches an expected capacity. That said, it is not a bad idea to employ backup magazines that have a few more rounds for you to have at your disposal.
The idea of defining your parameters of a fighting pistol should be defined by your experience, your knowledge of what your up against, and what may or could be expected of the pistol as far as performance. These are just a few of my own parameters that I have established for a pistol I would feel comfortable fighting with.