Yo, 'sup!
So I've been thinking about what the issue could be. Your information is correct - the bottleneck is showing outside the render system, which implies to me that it's not happening on the CPU's portion of rendering, but rather between the time when the main engine loop ends and when it picks up again. BDX's profiler only profiles inside of the engine loop, but outside the loop, I believe the GPU should probably be actually rendering, which is pretty much what should be expected by your earlier statement (that the game's using 30% CPU, so any slow-down is probably due to the GPU).
I'm not 100% sure what you mean by "see what shaders are actually running". The only shader that should be running on the title screen is the "normal" ubershader to handle lighting, texturing, etc.
I'm working on improving the profiler to show times where the CPU's waiting for the GPU to finish, which might be helpful.