Honestly I think the root of the problem is that the concept is weak and the class lacks a real niche that it owns.
This helps me put my finger on something about the binder. From the first time I read it, it left me cold, empty, and longing. To me its in the mechanics that it is weak and nicheless, and oh how weak and without niche it is. I read through the HoShadows binder part and could not tell what they did. They didn't make sense. The powers were 'fine' if not particularly inspiring (but thats how I feel about druids), there were class abilities that sure seemed like class abilities, but there was no hook where I could say "Oh, when you play this character you're going to be doing X, because of Y in flavor and Z in mechanics space". I've seen a few in play (very limited in D&D encounters, just two sessions with different people each time). The powers were nice. They work. But every other class has nice, working powers AND purpose, uniqueness, and interplay between powers and purpose. Binders don't get anything more than their powers, I've yet to see them use a class feature (such as pact boon), maybe shadow twist (actually i think they forgot to use it), and in that case, they're looking pretty weak and pointless.
And I've never seen them Bind anything! Where is the Bindage!
I think it was a class concept that really should have been axed, but at some point they must have realized they had nothing else to go with and a book that needed to be wrapped, so they went with it. Sometimes things just don't gel and the binder just didn't gel.
This I disagree with, though weakly. The concept has life. The idea that you're binding greater powers to yourself seems like it could be a smart take on the warlock schtick. Normal warlocks pledge themselves to willing patrons, binders bind a patrons power to themselves via ritual (or perhaps they bind themselves to the patron). This sounds like a go getter who owes their patron less, and is in more control of the pact. They chose/wrote the bargain and glued their patron into it. Maybe they can bind different powers to different chakras of their body or switch out who is bound to them (look at the vestige pact warlock for the concept of changing your pact benefactor) But nothing in the binder class suggestes this is being done, if anything they are more enslaved to their pact than a normal warlock, and gets a lesser share of warlock goodies to boot. The mechanics of the binder are devoid of any conceptual uniqueness and disjoint with any interesting concept. At best the concept of a binder seems to be "A shadowy version of an already shadowy class" and a shade of a shade is a shade too pale.
.....and the brain accidentally hit the ramble switch. This doesn't bode well for my day of work...