I see people bring up statement like "a lot of "optimal" choices are in-character knowledge, and common knowledge at that" a lot, and they really tend to ignore the very simple truth of reality. The "optimal" choices are not going to be as cut and dry in-character as they are mechanically to us players building the characters.
Take at look at the world today. Person X goes to buy a car. What car do they choose? How many people actually sit down and look at the size of the car, safety rating, average yearly maintenance costs, ect. and choose the car? Some. Far less than most. Just as many pick the one that makes them think "Ooooh Shiny" the most. More pick one similar to their last car/their parent's car due to strong emotional ties or simple brand loyalty (it's always worked good before, it'll work good for me too). Brand loyalty is actually a huge factor. It's why so many car companies buy out other companies and continue to use the old name too. Take a look at Ford for instance. They own Mercury as well. There Mercury cars are just Ford cars with a different emblem and model name slapped on. After that, we go on to features that can be added on, how the car will make you feel, how people will look at you with the car. Most often the only real factors people look at in such a purchase is "can I afford it" and that's actually even rarer than many would imagine.
So we hop to the Shadowrun universe. Let's take a piece of ware, let's say it's Reflex Recorder (Automatics). Now the corps say it helps a ton and they've even got endorsements from Military Personnel, Knight Errant Officers, hell even ex-urban brawl super star Greggy Mack is hyping it up. Down at the range though, you're not seeing that huge of a difference between those with it and those without it. 1/3 of a hit is not that much, and how many people with it are at maximum potential (thus being pushed over the normally capable edge by it)? A guy with a skill of 3 that tosses it in is just as good as a guy that has a veteran skill. Do people think there is a limit to what it will help? Is it not just as likely an elite trained or legendary trained guy will think "Joe has it and shoots worse than me, so why would I need it?" Toss some Muscle Toner in there, a Smartlink, a TacNet system, etc. and sure, some people will believe it's all worth it. Some people will believe that factor X, Y, or Z is responsible for all of it. Others will think only one or two factors are responsible for it. Why? Because some people just don't want to believe. Some people hang on to desperate beliefs. Others are just grouchy.
So, yes, the "optimal" choices are going to be known in-character, but there is likely just as much debate over what is best as there is today over how useful the 5.7 round is (what the P-90 and Five-Seven use) or whether the 9mm is better than the .45. There is no reason to think humanity has decided to peacefully agree on one opinion in 2070 on what is the best thing to have.
So sure, a character or two may agree that having every single little piece of equipment that can cram in is worth it, but to insist that all of them have to agree in-character through common knowledge that each piece is both beneficial and worthwhile just makes for some very simplistic characters. Either due to player knowledge just oozing down the edges or because they're dim-witted enough to believe every single add they see.
For a better example, there is a reason that equipment changes so much from precinct to precinct and even officer to officer in some cases. I've ridden with officers that carry a .45, officer's that carry a 9mm, officers that still rely on the old .38 special, and officers that swear by their Five-Seven. Each has it's own limitations and it's own benefits. Brands of Ballistic Vests change from location to location as well. Sometimes it's for environmental reasons (breathing in Florida vs. Insulation up north), but just as often it's because the people making purchases didn't have the same views at each precinct. Real life isn't mechanically defined to us like the SR world is to us. The SR world isn't mechanically defined to the characters like it is to the players. Sure, we can try to rationalize and usually find the "best of all worlds" in our RL purchases but we never know if it really was or not. That's not even getting into when the "better" product goes under do to marketing, PR, or other screwups. Industry standards are rarely the ceiling. They are usually much more cost efficient than that.
EDIT: For clarification the above is my play style. Not just a personal attack on anyone. More clarification in next post.