I think that your mistake was that you did not study the laptop User Manual very closely.
I find hard to believe that
When both cards work should consume more power.
I thought everyone knew that vendors build their HW with MS-Win in mind.
Your situation, translated to Linux, looks like you are switching computers HW on and off. This is new to Linux (automation mechanisms).
Since your system works well on the Hybrid mode, what is the real reason you want to use the dGPU-only mode?