So, I'll add my 2 cents in here since that's probably about all it's worth. I rank somewhere in the hobby category as far as Steel Beasts is concerned. Think I've been playing on and off for 3 years or so for what it's worth.
I have not mastered any if I'm being honest, however I think therein lies an important point. If I dedicate myself to learning the M1A2 fire control system inside and out down to using the backup systems that's all well and great, but I then join a TGIF game where we're using Leo's and CV90's. At that point I'm probably as "good" as everyone else since the basic function and key mapping for firing the other weapon systems are fairly similar, but my deeper knowledge of the M1 isn't helpful. Unless you're playing scenarios with specific equipment all the time, the game itself warrants more of a "jack of all trades, master of none" in this regard.
For those of us who didn't serve on these weapons, there is little incentive to get beyond the basic competency (unless you are really into learning it inside and out, which is totally cool if so). It doesn't seem that very often knowing how to use alternate/backup fire control systems is helpful since if your vehicle is in that bad of shape you've usually got more pressing concerns, if the vehicle is usable at all. Now, as I play more I am slowly picking some of this knowledge up, but as far as proactive learning it seems to me the time is better spent on tactics/employment/SA.
Retreat Route and Retreat Condition
To start, I knew the first and had a fuzzy idea of the second but had to look it up to make sure.
The bigger conversation here, to me, goes back to where you put your time in. Once I get done on the tank range and know how to do the essentials like lasing/computing lead, selecting the correct ammo, and firing effectively, the hard part begins. Frankly, shooting stuff is the easy part. Getting your tank to a good firing location without someone putting holes into it, and ensuring it can survive a battle or can egress if needed becomes the challenge. I'm an arty guy who spent half his career running patrols in Hummers and the other half driving around a goose egg in a M109. I have zero institutional knowledge on how to best employ a single tank, let along my platoon + element that I've just been given in a scenario. Figuring out how to best move my forces, what locations to occupy, setting up fields of fire, etc. has been my struggle. To that end I could probably do better learning the different tactics, routes, and whatnot that are built into SB to help me in that regard.
Intuitiveness (I think that's a word)
While I'm sure it could always be better, I personally think this is an area that SB does really well in. By and large, if you can figure out how to use one vehicle you can probably make do in most of the rest. Space is always fire. P is always compute/dump lead. The Function keys all generally work the same with views. Right click context menus are mostly the same. Yes, there are exceptions, but you learn them quickly. Some other simulation games don't do this *cough*DCS*cough* and it makes for a much higher learning curve.
Now, behind learning tactics and whatnot, the second biggest time investment for me in SB is learning how to get the game to do what I'm thinking in my head. I don't mean this to sound in any way harsh or negative as all games have this same requirement, but there is an element of fighting with the game/AI itself to get to the desired outcome. So far as that goes you start learning tricks or building habits that may not be tactically accurate, but get you the end result required.
As a parting shot I'll say this; what keeps me coming back to Steel Beasts is the mix of immersiveness and ease of which I can stay relatively proficient at it without needing a ton of spin up time between long absences. Crawling along in a tank or IFV knowing that enemy is near can really get my heart racing, and that's before the metaphorical crap hits the fan and it's an all out fight for your life. The excitement of springing a well planned ambush (or the dread of walking into one) is great. I think that's a pretty impressive accomplishment for something that was/is designed as a in depth trainer for military crews.