It's certainly a "feel" thing, and difficult to define, but comparing Slayer and Knight to PHB fighter, or Binder to PHB warlock, always gave me that feel.
Fair enough! The Trapper Keeper was pretty poorly made, sadly. There was a lot that was excellent conceptually, but the math just didn’t reach the basic numbers for the role.
Still, I think there was more good than bad, overall. The only real duds, IMO, were the Binder, Bladesinger (mostly after heroic, and mostly in that it only had at wills contributing to its concept), vampire, and arguably the Berserker?
The Fighters, Rangers, thief rogue; Mage, Executioner, Cavalier, Blackguard, and Skald, were all within pre-essentials power levels, and quite fun to play, for us at least.
That was the design intent. Delivering, on that promise, however.... (Most Essentials classes are vastly underpowered compared to their counterparts, and, quite frankly, some are virtually unplayable, or close to it, beyond Heroic tier, e.g. Binder, Bladesinger, etc.).
Furthermore, the lack of flexibility of build choice (compared to their counterparts) was galling to players who found this element of 4E's design a selling point.
Nah, none of them, except maybe the vampire, were close to unplayable at any level. They were “viable” for a CharOp game, but that isn’t important at all. They played fine in actual games, so long as your goal wasn’t to win dnd through superior system mastery (or you weren’t playing with people who were into that, obv). Except the vampire. It just...doesn’t work.
But the Binder was totally playable. It just didn’t have a clear mechanical identity, and tried to be a worse swordmage, both conceptually and mechanically, by not having significant power that blended magic and fighting. It just has cool at wills. What a waste.
But “vastly overpowered” is one of those phrases that only makes sense on a CharOp forum, tbh.