No, 'Geek the Mage First' is there for a very important reason. A mage can royally screw up a team's day if they don't have magic of their own to compensate. Sure, not all are combat mages or force-multipliers like illusionists or summoners, but you can't tell which is which until it is too late, so you geek them first. And if you can't spot a mage, your next priority target is the troll with the assault cannon. Sure, the stealthy assassin type or the street samurai may be the more dangerous threat overall, but you take out the mages and heavy weapons first because there's just too much at risk there.
Likewise, the 'Never deal with a dragon' trope is there for a good reason. When you deal with a dragon, you become part of their games, and their games are always about what is best for them. That's no different than being a corporate runner or on the payroll of the local Mafia family, but dragons have millenia of baggage that follows them around, usually with other dragons. Which means that, in addition to the stuff involving corporate politics, stealing magic artifacts, and influencing the locals, you got a good chance of going up against immortal elves and other dragons. Moreover, it is possible to outplay a corporate raider or Yakuza oyabun. Dragons are, literally, several times smarter than you, and have been playing these games for longer than most civilizations have been around.
Now, as far as drain versus shooting someone, you're right, Guns, if you're only considering one fight a day. But a smart runner doesn't plan on a single combat the whole run. They consider what happens if they have to shoot their way out of a situation, and still have more to do. Risking a few points of drain is fine. But when you've already got a few points on your condition monitor, those few points become more and more problematic, and you have to choose your spells carefully. Having a nonmagical attack option increases your versatility and stamina dramatically. That's why I always have at least two extra clips of ammo on me, even if my gun rarely clears its holster.