You can consider removing the interior, removing insulation and sliding out the bad Luan and sliding in new Luan after all is demolded and dry. As big a sheets that are manageable. Probably a little narrower than a stud cavity. Unless you can use Height, double up and then shift into position (if that makes any sense). You can always glue a second layer of luan where the seams are (mid stud) so mid stud there aren't any weak spots. Worse case is messing with the exterior on difficulty to fix cosmetically without paint et al that is lots more work.
You can also glue Pink insulation inbetween studs to the exterior luan that will provide further strength and help straighten the exterior fiberglass. Spray foam can make this worse as it expands in unexpected ways. If it pushes on the exterior (like if it gets between stud and Luan) then it can create a wave. I do use spray foam on side cavities the rigid foam inevitably has from misfit.
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)