Shaping curve object by curve (modifier) results in a terrible shape with cracked surface. Here is an extreme situation, but good visible issue.
How can I curve it smootly without adding more control points or remeshing?
Essential parts of successful deformation and avoiding other issues are
If a surface or shape isn't smooth enough increase Resolution U (Properties Editor > Object Data Properties > Resolution U). But first try increase deformation Curve, than Curve Object.