high vertex count for ModelEntity for custom geometry shader

I am translating an app I have created from Metal to RealityKit because it was too difficult to hand-roll raycasting and transformations in pure Metal AR application. Instead of rendering camera feed and point cloud data onto a MTLView via command encoder, I need to use an ARView (via RealityKit) so that RealityKit can power the spacial transformations of the AR objects.

I am trying to use Custom Materials in RealityKit to render the metal geometry and surface shaders on top of a plane. However, this standard plane only has 4 vertices. For my geometry modifier to work, I need a couple thousand vertices on the plane.

However, when I made my own custom mesh using the code from codingxr.com (below), there is so much lag when running the app. I need lots of vertices so that I can access these vertices in the geometry shader modifier.

Is there a way to create a performant many thousand vertices mesh in RealityKit?

Or is there a way to make Metal and RealityKit to work in the same scene so that I can render to a MTKView but also take advantage of the power of ARView?

private func buildMesh(numCells: simd_int2, cellSize: Float) -> ModelEntity {
    var positions: [simd_float3] = []
    var textureCoordinates: [simd_float2] = []
    var triangleIndices: [UInt32] = []
    
    let size: simd_float2 = [Float(numCells.x) * cellSize, Float(numCells.y) * cellSize]
    // Offset is used to make the origin in the center
    let offset: simd_float2 = [size.x / 2, size.y / 2]
    var i: UInt32 = 0
    
    for row in 0..<numCells.y {
        for col in 0..<numCells.x {
            let x = (Float(col) * cellSize) - offset.x
            let z = (Float(row) * cellSize) - offset.y
            
            positions.append([x, 0, z])
            positions.append([x + cellSize, 0, z])
            positions.append([x, 0, z + cellSize])
            positions.append([x + cellSize, 0, z + cellSize])
            
            textureCoordinates.append([0.0, 0.0])
            textureCoordinates.append([1.0, 0.0])
            textureCoordinates.append([0.0, 1.0])
            textureCoordinates.append([1.0, 1.0])
            
            // Triangle 1
            triangleIndices.append(i)
            triangleIndices.append(i + 2)
            triangleIndices.append(i + 1)
            
            // Triangle 2
            triangleIndices.append(i + 1)
            triangleIndices.append(i + 2)
            triangleIndices.append(i + 3)
            
            i += 4
        }
    }
    
    var descriptor = MeshDescriptor(name: "proceduralMesh")
    descriptor.positions = MeshBuffer(positions)
    descriptor.primitives = .triangles(triangleIndices)
    descriptor.textureCoordinates = MeshBuffer(textureCoordinates)
    
    var material = PhysicallyBasedMaterial()
    material.baseColor = .init(tint: .white, texture: .init(try! .load(named: "base_color")))
    material.normal = .init(texture: .init(try! .load(named: "normal")))
    let mesh = try! MeshResource.generate(from: [descriptor])
    
    return ModelEntity(mesh: mesh, materials: [material])
}