To be honest, neither of these are completely true, according to the science. Sometimes SM is a death sentence. It often will take years off a dog's life. It also is not always effectively treatable. Sometimes treatment only gives weeks, months or a few extra years, and either option (surgery of medications) is completely uncertain in result and effectiveness, for the entire lifespan of the dog.
This is why a diagnosis is always a shock, and knowing your dog has this condition is a serious blow to any cavalier owner. An owner always lives with that uncertainty and the challenge of managing a condition that almost always progresses if using medications alone, and there are only a limited number of similar medications to choose from (hence the 'cocktail' approach as usually there are combinations that work better for a given dog). Even making the choice of treatment is difficult and most of us regularly weigh up if we have made the right choice. There are no clear choices.
At the same time, many dogs live many years, even a full lifespan, with SM. Dogs can be mildly or seriously affected. Occasionally it doesn't really seem to progress or does so slowly. I can say to anyone with a diagnosis that often predictions on a given dog are wrong, for better or for worse.
I do not think it right for people to start to consider SM as a manageable condition with lots of treatment options and that is why I do not want to falsely airbrush the condition as it isn't fair to the reality for owners. In some dogs, SM can indeed be managed well. In others, there are regular and frustrating ups and downs. For an unfortunate some, it's a difficult, hard to witness battle.
I know Soushiruiuma is aware of all of this and know she also is aware of the many dogs here with SM and how they and their owners have managed. There are good stories and bad. We'll all be hoping this is a case that can be managed, and medications can give very quick relief, but do not halt progression.
On syrinx size -- Soushiruiuma, there are several studies that suggest length isn't as much an issue as width and position. Neurologists sometimes see dogs with mild symptoms and syrinxes running the length of the spinal cord. Of course you are seeing several symptoms at the moment but don't lose heart at length alone. :flwr: