As much as Ves did not think highly of the Monster Slayer's potential to become a living mech, he did not rule out the possibility entirely.
There were always exceptions. Humanity's mech industry was incredibly vast and diverse.
When Ves visited the Masterwork Gallery in Chance Bay, he personally confirmed that every exhibit possessed varying degrees of X-Factor.
This was something inherent to them due to how much emotion and effort their makers had put into their design and fabrication. The mech designers literally imbued their work with a portion of themselves. This was probably the basis for making their machines alive, if only faintly.
The mechs probably wouldn't experience any further growth unless they became affected by exceptional circumstances.
The most obvious way for mechs to become more alive was to be used by a mech pilot that was breaking through!