Isn't it the 'legacy' systems are supposed to be left operating as-is, almost like black boxes with defined properties? Some kind of a known seam in the process. Meanwhile, all extensions to process are to be handled by other means.

Given the current capacities, there could be additional layers added to filter or enhance whatever comes out of the legacy processes.

Sure, there needs to be a "keeper" for those legacy systems, but migrating off them may be asking for too much of a manager's beef to get an approval to accomplish.