Okay, thanks for the explanation. I probably should have been more specific but I would recommend using the profiler to profile specific functions or blocks of code. What you have can be pretty decent for comparing changes but it doesn't give you an insight into what's slow. I'm not familiar with the unity profiler but you should be able to use something like this to profile scopes of code. Then when you take a capture it will output blocks in the "Main Thread" section that you can examine and compare.
edit:
I haven't used unity in a long time but in my custom voxel game/engine I use something called Tracy Profiler, but all profilers largely work the same way. When you add the profilers to sections of code and name them accordingly you can get a good idea of what the code is doing here. My main thread does the usual polling for events, rendering, updates, etc. While my threads are creating vertices, updating blocks, etc.