I think this is spot on considering a few of what must be ‘easy fixes’ like the long time and reported a lot bug with splitting meshes that are disjointed with disjointed parts disappearing: https://mcneel.myjetbrains.com/youtrack/issue/RH-31155
This not being fixed is a clear example of even basic mesh operations not being a priority @ RMA despite a lot of reports and reasonable requests.
I’m sure there is a deeper core work to be done too to make it perfect with mesh booleans on more complex on not clean meshes, but we are still missing a lot of basics.
I did my part of convincing and listing the obvious shortcomings here: More Mesh friendly Rhino A few of them were addressed in V6 but still hope some more basic ones could make it to the V6 release so we don’t wait another 5+ years for the much needed improvements in that area. Rhino is well beyond NURBS modeler now and for a mature and versatile tool like that it is still surprising to see some basic problems and lack of mesh-related functionality.
@RIL - many times I would use MeshToNURB if mesh splits/trim fail - the chances of surface cutting commands working are much higher. Then convert back to mesh. In your case though with more dense meshes it most likely will not be a viable workaround.
–jarek