That's a tough one, because the Zoldyck butler system feels deliberately designed to crush personal ambition into a pulp. They're basically raised from birth to sublimate any individual desire into perfect service. A lot of stories show servants rebelling, but the Zoldycks are different – their loyalty isn't just a job, it's a core part of their identity, almost like a cult. Look at Canary. Her ambition wasn't to leave or get a better position; it was to be worthy of the family's trust, to master her skills to the point where she could protect their interests. Her personal drive got funneled right back into being a better asset.
You see it with Gotoh too, but in a colder, more analytical way. His ambition might be expressed as maintaining the estate's perfection, optimizing security protocols, or being the most efficient manager possible. It's still a personal goal, but it's completely aligned with the family's needs. The balance is an illusion. The 'balance' is their ambition becoming synonymous with flawless execution of their duties. Any deviation from that, like a butler wanting to start their own business, would be seen as a catastrophic failure of conditioning. It's kinda bleak when you think about it.