You don't think there's a risk of a heavy door pulling on the joint?
With the one that's not damaged all the way a sort of wedge shape like this seems like it would give more mechanical strength. But unsure of how you'd do something with the door that's fucked all the way to the top.
Maybe don't make the new piece so you screw exactly between old and new, and carefully use nice, long enough screws to fix hinges.
But if the surfaces are even on the new and old wood and you clamp properly, it will be very strong.
Router/chisel out the doors so that the "hole" is uniform.
Glue in some oversized pine using PVA and cramps.
Plane flush, then fit hinges.
The glued timber, if done correctly, will be at least as strong as the original.