It would help against attacks that depend on corrupting process address space, like this one.
Additionally, one could use OS security features to reduce API surface for each plugin, depending on what they are actually supposed to be doing, e.g. no need for file system access if they only do in-memory data processing.
As for "would it help in 100% of the attacks?", no.
Even if there were no plugins support, there is still the possibility to exploit logical errors anyway.
What matters is having a balance between reducing attack surface, and application features, and it than regard process sandboxing is much safer than loading foreign code in-process.
Additionally, one could use OS security features to reduce API surface for each plugin, depending on what they are actually supposed to be doing, e.g. no need for file system access if they only do in-memory data processing.
As for "would it help in 100% of the attacks?", no.
Even if there were no plugins support, there is still the possibility to exploit logical errors anyway.
What matters is having a balance between reducing attack surface, and application features, and it than regard process sandboxing is much safer than loading foreign code in-process.