i can confirm the outlined behavior of the initial post. I have not started using brave as my main browser since it is causing my system to permanently use about 20% of my CPU.
This behavior has been there for some months for me.
I am running Windows 10.0.18363 and Brave 1.2.41.
Also attached a screenshot with 3 tabs open showing the CPU usage.
update: same pc booted into linux and the cpu usage is much better ( 2-10 % with 1 tab open) The ledger service however is at 0%, so i cant reproduce it on linux right now.