Even if the Gloom-shrooms are destroyed by Jack-in-the-Box Zombies, 4 Cob Cannons and any instants (Squash, Cherry Bomb and Ice-shroom) is still good enough to sustain the weakened row 2 or 5. You can just let the game run by itself and moderate the build sparingly.
The build can handle Zombonis and Gargantuars finely, although not Giga-gargantuars and Balloon Zombies.
Traditional 4 Cob Cannon builds are versatile and slow-paced. Therefore the build is less stressful on repairing defenses while requires a slightly more precise timing for the 8 Cob Cannons. The need for maintenance due to Digger Zombies is reduced significantly and Tall-nut is maintained for Dolphin Rider Zombies. Here is a low maintenance version of the setup.
The flower pots are optional and contribute nothing significant.