To be reliably secure against medium complexity attacks I'd argue that training and sims form a valuable part of defence in depth.
If you can tune those low(er) cost services to deliver a, say, 30% benefit in reducing vulnerability to more targeted attacks like those targeting internal changes or vacation allowance (which suggest) a level of bespoke targeting, you're already delivering a very meaningful risk reduction for the business.
Beyond that, it's careful access control design, containment and resilience, reduction in blast radius though tight permissioning, auditability of actions, etc, right?