Export Discretized ImplicitRegion as step using OpenCascade

Following the reply by @user21 to this post on exporting a region to a step file, I tried to do the same for a Discretized ImplicitRegion, but OpenCascadeShape didn’t appear to work. Is there a switch or a constraint I need to apply to Discretized regions to allow OpenCascadeShape to handle them?

imReg = ImplicitRegion[x^2 + y^2 - z < 0, {x, y, z}];
discReg = DiscretizeRegion[imReg, {{-2, 2}, {-2, 2}, {0, 5}}]

Needs["OpenCascadeLink`"]
shape = OpenCascadeShape[discReg]

OpenCascadeShapeExport["~/shape.step", shape]

Needs["NDSolve`FEM`"];
Needs["OpenCascadeLink`"]
imReg = ImplicitRegion[x^2 + y^2 - z < 0, {{x, -2, 2}, {y, -2, 2}, {z, 0, 5}}];
bmesh = ToBoundaryMesh[imReg];
bmesh["Wireframe"]
shape = OpenCascadeShape[bmesh]
OpenCascadeShapeExport["~/shape.stp", shape]