The practical answer
The safest approach is often incremental: understand the system, identify the most expensive constraints, expose better interfaces and replace fragile parts in controlled steps.
Questions teams ask
Why avoid a full rewrite?+
Rewrites can discard years of working business logic and introduce a long period where old and new systems both need attention.
Where should modernisation start?+
Start where change is most expensive: tightly coupled code, difficult deployments, missing APIs, weak testing or workflows that block the business.
How does AI fit in?+
Modernisation can make existing systems easier to connect to AI through APIs, cleaner data access and better separation of responsibilities.