To be honest, he's right about navigation problems. Hydro is poluted with massive flashing signs and people still walk the wrong way.
Nobody plays hydro because it's impossible to "learn". The concept for TC was that it forced players into battles where they couldn't just "rinse and repeat" the same old tactics like say if they were to join a 2fort 24/7 server, where players would join the game and immediately know what class they want to be, what tactics to use and where.
Players spend half the round just figuring out where the enemy control point is, let alone fighting through enemies to eventually capture it.
TC just doesn't fit the same play style as any other TF2 mode; one of the things that makes TF2 so comfortable to play is its simplicity and TC throws that down the toilet, so it's unsurprising then that the majority of TF2 players dislike it.
TC isn't so much a broken mode, it just doesn't compliment the average TF2 player's attitude to gaming. Which is usually playing the same map over and over (Why 24/7 servers are way more popular than others). Valve even acknowledged this trend (hydro commentary) in gamers across the whole industry (so i guess it's ironic then that their response to this specific fact was something of a complete and utter failure).
edit: TC could be worked into a form that allowed players to better comprehend their roles, with more consistant pathing; but then you're defeating the purpose of TC. It'll just be like several push maps rolled into one map and split into rounds. Which is just annoying for players because it breaks flow, not to mention a waste of effort for something that could otherwise be 2 or 3 unique maps.