You're picking the X, Y, and Z components from different unrelated positions as each call to GenSpherePointCorrect makes a completely new position.
You need to generate a single Vector3 each loop iteration and assign its components to the vertex position.

Vertex vertices[1500];
for (unsigned int i = 0; i < 1500; ++i)
{
  vertices.Color = (const float*)&Colors::Red;
  vector3 vertex = GenSpherePointCorrect();
  vertices.Pos.x = vertex.x;
  vertices.Pos.y = vertex.y;
  vertices.Pos.z = vertex.z;
}
	

Alright KburtHard84,Zao, I seem to get it working now. Thx

It's much faster to just generate random points in the unit rectangle, and then discard all points outside the unit circle

Vertex vertices[1500];

for (unsigned int i = 0; i < 1500; ++i) {
  float xpos, ypos;
  while (true) {
    xpos = rng.RandomFloat(); // EDIT: This should give a value in the range [-1.0, +1.0]
    ypos = rng.RandomFloat();
    if (xpos * xpos + ypos * ypos <= 1.0) break; // inside unit circle, done!
    
    // else try again
  }

  vertices[i].Color = (const float*)&Colors::Red;
  vertices[i].Pos.x = xpos;
  vertices[i].Pos.y = ypos;
  vertices[i].Pos.z = 0.0f;
}

cos, sin, and sqrt computations are expensive (although sqrt not so much anymore).