I believe that is partially true...
You're close when you say "lack of novice training is shrinking the pool", however, it's more than that. It's more the overwhelming aggression of large alliances that are pushing new players away, and veteran players who started playing as youths tend to grow up, get jobs, get married, have kids, etc., etc..
If the veteran players still playing hope to see the player base expand, then they ought take more interest in the players who manage to progress their Polis above 2500 by the time their Battle Protection ends, rather than greedily devouring them. Benevolently communicating & engaging with new players will nurture a player's interest, and give them a more enjoyable gaming experience, which in turn, would likely cause them to continue playing, and introduce their friends to the game as well.
Having said that, it's my intention that when the next US server starts, to establish a training alliance. If anyone here would be interested in joining me on this endeavor, please, add me so that we can exchange email address to send invites for placement in the next US server.