The attack of ONE Recon Titan assisted by the Legion is something the future generations will not fully understand. Maybe this decision was made for political reasons; lets show that we can do at least something.
The Legion commander, however, made two right conclusions from this situation. 1. Titans are the weapons for this war. 2. One Titan has little value if any.
That is why the Legion recruited a large force of Titans as soon as they became available. The Warhounds provided good batlefield intel and made a strong advance guard the Legion lacked until then. The Reavers followed, taking out the unfortunate Orks from safe distance.
By the way, the first attack of a Titan was the only time Orks used their Gargants correctly. They brought several Gargants to fight one Recon Titan and I do not believe, whatever the Comissars say, that the Titan took out any of them. Even a Reaver could not kill a Gargant facing several enemies. In later battles, however, the orks spread their Gargants over the whole area and my Titan force met one Gargant at a time. All that maters in such situations is longer range and concentrated fire. Sometimes a desperate Gargant attacked hoping to use their short range weapons; the Titans retreated and fired again from safe distance. I have never seen a Gargant vs Reaver duel in two campaigns! It takes about five Reavers firing two shots each to kill a Gargant, so, the fighter of the Metallic Legion was by all means a hero, he had no understanding of tactics whatsoever.