Unfortunately there is no magic pill to solve this basic law of physics. The way you have your model set up, you’re relaying on layers being deposited in the z-Axis. There really are only two tools in the “printer/slicer” tool box to address smoothness and both are blunt instruments. Then there is post-processing of the model itself. I’ll cover the first.
Category 1: Slicer settings
Tool #1: Layer height.
The lowest layer height supported is 0.08 as you probably already know. That will give you the best possible resolution for a 0.4 hotend nozzle.
Tool#2: Optional 0.2 Hotend nozzle
Whereas this will effectively double your resolution, it will not make it perfect.
Category 2: Mechanical post-processing of the model.
- Sanding - Needs no explanation.
- Filler and sanding - Just like performing body work on a car. Use putty glaze(which is typically red) to fill in the holes. Then sand smooth and coat with paint.
- Chemical smoothing. For ABS filament, acetone is the solvent. For PVA filament, Isopropyl Alcohol is the solvent.
There are literally hundreds of YouTube videos on this topic. Virtually every single one in my view is 80% clickbait and 20% substance. Why do I say that? Because they show a nice very glossy thumbnail of a shiny object, only to reveal that all they did was apply a surface smoothing finish of some type. This is hardly what we are looking for, isn’t it. These videos in my view are a big nothing burger. Here’s the search term for them but they may give you ideas.
https://www.youtube.com/results?search_query=3d+printing+smooth+surfaces
This one video is probably the most honest in that this person who is a model maker doesn’t hide the fact that he just uses paint, sanding and fillers to achieve his look. https://www.youtube.com/watch?v=xxdjFREJpKs
Here are some of the thumbnails that I was referring to that are more clickbait than substance.
Baby powder technique then just using UV curable resin. Hardly a solution. https://www.youtube.com/watch?v=KVf0mbBCygQ&pp=ygUbM2QgcHJpbnRpbmcgc21vb3RoIHN1cmZhY2Vzhttps://www.youtube.com/watch?v=KVf0mbBCygQ&pp=ygUbM2QgcHJpbnRpbmcgc21vb3RoIHN1cmZhY2Vz
Sanding and auto body putty glaze. Probably the more honest of videos. https://www.youtube.com/watch?v=xxdjFREJpKs&pp=ygUbM2QgcHJpbnRpbmcgc21vb3RoIHN1cmZhY2Vz
My best cheat method that I’ve used. Glaze Spray Paint.
I use a simple technique for my smoothing. Purchase any triple-glaze spray paint, they make it in both gloss and matte. After printing at 0.08 layer height, sand down the surfaces. I recommend printing at 4 walls which will allow for enough extra material so that you don’t accidentally sand-through. Then spray paint and you will have the best solution.
https://www.amazon.com/s?k=Triple+Thick+Glaze
Reorient the model in vertical mode.
You will always get the best results if you tils the model at an angle and use supports. This is a very, very, very did I say very? Time consuming, long and trial and error process to find the optimal angle.
Here’s an example.
Note however, by changing the default angle and using tree support I can get some relieve from the contouring affect that you desire to remove but not 100%.
Then there is the line width Parameters which can also help - to a small degree. If you are already printing at a 0.8 layer height, this parameter won’t make a difference but I note it because it can help you if you want to speed up your print and only slow it down for the outside lines.
The limits of what’s possible with FDM technology.
If you want to see what is possible using a combination of slower print speeds, post processing and finally polishing and glazing. There is no better example than the optically clear thread that was posted last year.
Although I was able to get some startling results. It was really in my opinion a parlor trick that relied on as much post processing as it relied upon profile tuning. Here is one example of the possible results. a 25mm cube with obvious clear but not perfect, optical properties.
Last Option - Smooth the model using a 3rd party mesh tool like Meshlab, Blender or Windows 3D Builder
While this will give you some measure of smoothness, it will be at the sacrifice of detail and may only give you some relief. In the end, you are limited in making fat filament skinny. 
