To some it is. Doesnt mean you're wrong, but some groups consider it key. And it is priceless when a runner pulls a trigger and gets nothing because he skimped on smartlink and basic math skills.
Or pops a narcojet capsule/gel round into that lock because it completely skipped his mind to switch mags while he was balls to the wall running from that Firewatch team.
Goal being for draining fun out of combat... Goal for "realism"... Same thing. It's a game. Uber realism being injected in is the antithesis of fun,
Which is perfectly valid if you add a "to me" to it, but it is an
opinion of yours, not a fact. Some of us like the challenge of actually playing a realistic game. There are plenty of games out there that allow for much higher action movie antics. I prefer my SR a perfectly brewed mix of grit and dystopia. Allowing the movie gun clips that never run out of bullets is pretty much the opposite of that feel.
and no, ammo tracking does nothing to the 'balance' stuff. "Balance" is just something that gets pulled out in efforts to make the PCs weak as little kittens in comparison to the opposition.
I suggest actually taking a few seconds, seriously just a few, to head to Google and take a gander at game balancing. Balancing is a required aspect of games, otherwise it becomes a sole matter of what is liked the most wins and everything else (stats, dice rolls, etc.) is irrelevant. It's pretty much the opposite of what you've stated, in a world undeniably oriented to opposed the shadowrunners, balance is what keeps them able to compete, because whatever they can do, corps can do bigger, better, and with more explosions.
As for the actual ammunition balance, you seem to have completely jumped ship and missed the entire point of
how ammunition plays a factor in balance. It's not an issue of runners vs. opposition, but gun A vs. gun B.
Let's take the sporting rifle for example. If ammunition is "infinitely loaded" with no need to track, then why would you take any of the rifles other than the Elephant Rifle (using the core book only for the moment). The cost difference really is a non-issue in the great scheme of things and 10P (no point in not double barreling it every shot with no ammo tracking) -1 is leaps and bounds better than 7P -1.
To say, in effect, that all balance is just there to make players "weak as kittens" is just blatant willful ignorance. Now, there is a difference between system balance, and a GM being a douche and calling it "balance". That doesn't mean that the system balance is bad, but that the GM is bad. You can't fault the car for having a shitty driver.