I'll start by saying that I'm really surprised that that there aren't Chinese or Taiwanese knock-offs named "Slemer." As far as I know, at least.
Hey, Dan. How ya doin'? I'll address a bit more on clarinet.
Anyhow, there are extremely few orchestral parts that call for alto clarinet. Most of the time, when you see an alto clarinet part in a high school band or community band, it's going to be doubling some other instrument. I'm pretty sure that Selmer realizes this. Simple supply and demand: you want a
new professional-level alto clarinet? Well, you've got your Yamaha YCL-631 at $7K, the Selmer at $12K, and the Buffet at $14K. I'd also be surprised if Yamaha, Selmer, and Buffet, combined, produce more than a few thousand alto clarinets a year. It might even be just a few hundred. Also, remember that the unpopular pitches of clarinets (usually) get the updates found on a Bb soprano last. So, it might take the unpopular professional alto clarinet a few years to get the same updates.
Note that the reviewer is a rather big-name player and professor (IIRC). He's a bit of a Selmer fanboy -- which he should be, because he's got a $15K Selmer bass clarinet and a bunch of other high-end custom Selmers -- but he's given some very fair reviews on rather inexpensive horns, too, like the Kessler bass.
Selmer has tried lots of interesting clarinet designs over the years. Off the top of my head, take a look at the
Marchi System clarinet. There's also the
Mazzeo System. I might as well
just link Selmer's article.
I think Yamaha's presence in the clarinet market has helped a lot. They keep improving their soprano clarinets and that forces Selmer and Buffet to keep up.
In any case, the major problem I have with Selmer's pricing is on their saxophones. They've been competing with themselves in the used market. Not just with their Mark VI, but with used Super Action 80s, and their Reference horns. Those horns lose their value very quickly. I'm more likely to pick up a
$4600 Reference 54 open box from a reputable dealer than buy a new Reference 54 for $6900.
FWIW and, obviously, IMO, the horn that "turned saxophone design on its head" is the Super (Balanced) Action. It's mainly the keywork design, not the bore improvements. I also think you could successfully argue that the design that launched a thousand ships is the Balanced Action.
Finally, I should say that I have no particular allegiance to any make/model. I generally recommend people get used Yamaha saxophones and clarinets because they're good value. I really enjoyed playing Selmer Mark VI saxophones and I liked my Selmer clarinets. That doesn't mean that I think you "have to" buy one or you're not a pro.