First, wasn't a personal attack; more like a hand buzzer to try to get you to do a double-take at your own stuff. While I was going to chop everything you said up and do a point-by-point debate, I realized that it wasn't necessary.
What it boils down to is this: not only is a dragon a living, flying, spell-casting tank, but it is a cut-throat supergenius (minimum Logic and Intuition attributes of 8 each) with a crystal-clear memory (literally at times) and an eye for any and every advantage, weakness, hesitation, or other point of leverage its opponents display. It by nature and habit takes the long view, regarding a 'short-term plan' as one that wraps up within ten or twenty years, it never forgets a slight, and makes absolutely certain that it not only 'lives well' as the best form of revenge, but also makes sure that the life of whomever hurt or insulted it (except, perhaps, another dracoform of equal rank) is turned to both its own benefit and is ended prematurely. It is insatiably drawn to power and the ruthless use of it, acquiring millions, billions, and possibly trillions (or more!) of nuyen in assets, all to serve the interests of one being: itself.
Now, you argue that this is no different than any other corporation or syndicate, and to an extent, you're right; the Mob has a long memory, the Yaks don't play that sort of game, and screwing with a megacorporation is a short road to a long rough patch.
In time, however, most metahumans forget; they can forgive, or have their forgiveness purchased. They don't generally make plans that include 'make Gerald's life a living hell' as an aside that keep 'Gerald' in poverty and anguish for most of a decade, whacking his legs out from under him -- possibly literally -- if he manages to get a leg up. There (likely) isn't a file folder that says 'Making That Gerald Guy Pay For Looking Scornful When I Said That One Thing' in the cabinet of a corporate CEO. Most groups -- especially corporations -- have to serve the bottom line, and so the vast majority of activities pursued by them, whether that's at the behest of a corporate Johnson, a power-player, or the CEO (or a made man or the Don himself), have to serve that bottom line. In some situations, yeah, that's gonna be 'Jimmy the Fink done did us wrong; go make an object lesson out of him.'
But that still isn't 'Jimmy the Fink done did us wrong; let's wait six years, then blow up his car, burn down his house, whack his wife making it look like a traffic accident, plant a sympathetic hooker on him, get him to turn himself into a mule for the organization by way of a couple/three cutouts, and after eight months of running CalHots, see if we can't set up a link into Tir Tairngire, using him as the mule for it. He gets nailed, fine, the elves will roast him over a slow fire. He doesn't get nailed, fine, we got a pipeline into the Tir.' This latter is the way a dragon thinks.
It just popped into my head, someone in a movie that a) actually resembles a Shadowrun dragon and b) has earned the reputation for it: Terry Benedict, from Ocean's 11. "The last guy they caught cheating in here? Benedict not only sent him up for 10 years, he had the bank seize his house and then he bankrupted his brother-in-law's tractor dealership." "If you're gonna steal from Terry Benedict, you'd better goddamn know. This sort of thing used to be civilized. You'd hit a guy, he'd whack you, done. But with Benedict... at the end of this, he'd better not know you're involved, not know your names or think you're dead, because he'll kill ya, and then he'll go to work on ya." Because this is what dragons do -- their vengeance tends to be all out of proportion to the scale of the insult.
In addition, dragons are -- even at baseline Charisma 8-9 -- compelling and competent negotiators. Which means that the likelihood of there being a mild-looking sub-clause that will mean the dragon can sell your organs if you screw up is pretty damn high, even if the 'contract' was verbal-and-a-handshake. (See 'out of proportion vengeance', above.)
Which is why the advice is to avoid cutting a deal with them, or better, don't deal with them at all. Because, see, a corporation or syndicate -- which are collections of individuals -- require multiple people. To be mastermind, to be negotiator, to be legbreaker, to be mystic, to be historian, analyst, accountant, everything else. A dragon ... can be all of those himself, if he so wishes. They don't always wish; 'exercise of power' means having minions, and making those minions do things. But the information his organization collects does get to the dragon, and the dragon does put two and two together, faster and in ways different than people do, and holds onto that information far longer -- and then puts this 'two' together with a 'two' that happens ten years down the road, and winnows out a secret that is otherwise incredibly well kept.
Can people do this? One or two of these roles, yeah, sure, but even people who can do that are few and far between. All of them at once?
"Well, that's what you have the corporation for."
Yeah. Yeah, that's my point. Because a dragon with the assets of a corporation, but not the people, pretty much is a corporation -- because he is, simultaneously, all those people at once. Does this have limits? Of course it does!! But a dragon's limits, a dragon's 'point of failure', are far further out, in many many more directions, than any single metahuman -- and than most groups of metahumans, if only for the simple fact that a dragon that owns a corporation can and will do things that harm the corporation in order to achieve a 'point of satisfaction' understandable only to him.
In any case. If it's not good advice in your world, then that's the way your world is. You're 'thinking for yourself', which is good. But the way you're thinking of dragons isn't the way dragons are canonically thought of in the Shadowrun universe, for all the reasons given so far.
Otherwise, good luck, have fun, tell us how it works out for your players. Or, well, for you, if you're a player and your GM doesn't buy in to your 'dragons are nothing to be feared, respected, and kept at arm's length' philosophy.