Then it is not that different from blocking symbol markers with destructible terrain like Pianos and Ice Pillar isn't it. In most Symbols game with one side playing Zipp I played or watched, there usually is a symbol or two protected by a turn1-created Piano remaining not touched by enemy until the end of the game. Players are unlikely to score full point in a game anyway, so why bother to go to the symbols behind blocking marker, whether destructible or not.
I believe you need to block all 4 symbols by turn 2 before enemies can get into any one of them, otherwise it is not as impactful as it may sound.
And again, careful defining the terrain can help to resolve the issue a lot. For instance, we can defined all impassible terrains as climbable, and suddenly Hoffman cannot shut down the center line with a train, nor he can trap a model with a wall.