Venerable Orthox De Massie was by far the most threatening known quantity in the enemy mech force.
Any mech pilot who fought during the dwarven rebellion were truly battle-hardened. The conditions for the rebel soldiers back then were so difficult that they had to rely on grit, determination and a willingness to sacrifice a lot of lives in order to defeat the established human powers.
As a survivor of this meat grinder, Venerable Orthox not only managed to survive the war, but thrive during the period of rapid growth and consolidation. Being able to strengthen his will during times of peace was a clear indicator that this was a warrior who never gave up and always prepared for the next fight even if it was decades away!
Every mech pilot who managed to grow stronger did so because they thought it was necessary. This was easy to maintain in times of war but a lot harder to sustain when there wasn't an obvious need to fight.