Leman Russ outside the Siege of Terra

Would Leman Russ and his legion have been more useful defending Terra during the siege?

Their presence would strengthen the defenses, but it would remove the disruption and information gained from operating outside the siege.

In the Warhammer 40,000 scenario, bringing Russ and his forces to Terra would add strength to the defenses. Keeping them outside allows attacks on the besiegers' movements and disrupts their plans. Those operations can also pass information to other loyalist forces. Moving the legion to the walls removes those outside effects, so additional defenders do not automatically produce a better result.