Monogame is missing a lot of features if you're wanting anything but the basics in 3D (it's still very good for 2D games). I tried hard to use it instead of Unity (for over a year), and only recently switched to Unity because I wanted to add VR support, and forgot just how much easier doing 3D in Unity is compared to Monogame.
Like I was fighting Monogame on model rendering, textures, shaders, cross-platform (never could get a high-res 3D working for the Mac version), anti-aliasing, etc. Everything 3D was being a pain in the ass to get working, and my progress was very slow.
After one day of porting my assets over to Unity, doing some tweaks in the editor, and importing a few assets from the Unity store, and my game already looked better than it ever looked in Monogame (still working on porting the rest of the game).
It should be said that I'm not an expert 3D developer, I'm much stronger in 2D, but have been trying to do more in 3D lately, and that may be part of why I struggled with Monogame in 3D. People who have no issues coding in OpenGL or DirectX directly probably won't have as many issues as I did.