OK, that might not be the perfect solution, but hopefully this helps.
Multiple things should be adjusted.
1. Let's change vertices where material ID changes to Bezier.
2. Add empty Corner Segment
3. Set Default Mode to Adaptive And Corner Vertex type to Bezier. Bevel mode to None.
4. Adjust Curve Steps to 80
5. Optional. Might be needed, might be skipped.
To flatten a gap that forms on First Spline vertex We can set Vertical Deform on both geometry settings.
There will still be small gap. Hopefully this is acceptable. If not YOu can add Welder Modifier on top of RC object.
Hope this helps.(C) Paul