What you were doing first was fine, it's the smoothing group that is causing those nasty edges and reliance on normal map to smooth those outs. To get rid of that seam you need to have those edges stitched together. To get rid of the wierd shading with that inset inside the column, you need to separate the smoothing of the…
You really need to smooth out the the main forms (circle at top and base) as the silhouette is very jagged right now. The rectangular insets could perhaps use a bit more geo as well. The black circle above the big rectangular inset could probably be removed and be faked with the textures as it doesn't change the…
https://youtu.be/7gMHH2Z5WeE A brief quick demo on new modeling tools i have been developing. Some useful selection tools and a Inset face tool which works with single side face shells. Tools covered: Grow Face By Angle Grow Edge Ring Shrink Edge Ring Face Fill Select Inset Face
Kinda seems like you are over complicating the shape from the get go. The curve you are talking about looks more like the bottom half of an inset. I would try modeling the entire block under the scope, add the inset, then if need be, split the top half of the block at the seam.