The legacy foreman_hooks plugin provided full access to model objects that the webhooks plugin does not intentionally provide.
The scope of what is available is limited by the safemode and all objects and macros are both subject to an API stability promise and are fully documented.
The number of events triggered by webhooks is substantially fewer than with foreman_hooks.
Webhooks are processed asynchronously so there is minimal risk of tampering with internals of the system.
It is not possible to migrate from foreman_hooks without creating payloads for each individual webhook script.
However, the webhooks plugin comes with several example payload templates.
You can also use the example payloads with shellhooks to simplify migration.
Both script and payload templates must be customized to achieve similar results.