There's a difference between "inherently difficult" and "difficult to update this software package". My reading of this thread is that the MS devs are saying this will take them a lot of effort to implement in this app, not that the new implementation could be simpler than the existing implementation. Asking to rearchitect the application is an involved process which would take a lot of back-and-forth to explain the tradeoffs. The new architecture can be simple, but evaluating a new architecture and moving to it are not.

There's a point at which you've moved from "fix this bug" or "evaluate this new component" to "justify the existing design" and "plan a re-architecture".