When Ves learned that the second major cultivation rank was mainly about cultivating one's domain, he knew that it would play a large role in his future progression.
It was not difficult to assume that the main reason why many Master Mech Designers failed to advance to the rank of Star Designer was because their domains did not meet the exceedingly high standards!
A more complicated domain granted Ves more options, but also weakened his focus. The choice to go for this reward was a double-edged sword for that reason.
Ves still felt tempted. It was a great opportunity to increase the versatility of his works and make them more fault tolerant.
That was not to say it was impossible for him to design mechs without resorting to this option. He was doing pretty fine so far. He just wanted to do better. Taking risks and enduring greater hardships in the hopes of obtaining a greater payoff.