Sometimes it isn't really a problem of team work it's just a problem of DPS. The window to attack Crota and the margin for error are so small that if you don't have enough DPS you'll never bring down his shields fast enough. Team work is great and it was essential for the Vault but Bungie made CE a giant gear check and that's about all it is really. Instead of making a new raid that was interesting or required you to strategize they simply upped the enemy levels, threw hoards of enemies at us, and added enrage timers to the bosses. It's a prime example of lazy design being covered up with artificial difficulty.