Actually, the dendrobium looks too small in that pot. i think the pot is fine, just new media. I am if-y on sphagnum. Its great, but it decays and holds too much moisture. I chop my up and mix it with bark (along with charcoal and perlite).
I have found that my monilforme type Dendros don't really sulk (for me.) Once they get pot-bound, they seem to pop out buds as they are supposed to.
Some good news Ross. During today's photo session I noticed the development of a new cane. I'm relieved. The slowness in development may have been due to climate change or delivery conditions. You never know what plants actually go through before you receive them.
I purchased a Den. Spectabile last September by mail from Puerto Rico. Looked healthy and well potted when I got it so I left it alone. It then proceeded to do absolutely nothing until June of this year when it sent out two new canes. It's humming along now. Must be a moody plant.