I'm almost always plugged in when using ethernet, so power is of no concern. Heat is a different matter, but Apple have historically been good at finding solutions to problems so they are first to market, or first to market with a working solution.
It’s been SEVEN YEARS...onboard GbE is not coming back to the MacBook Pro, ever. Buy the adapter and move on. Apple made concessions on the 16” MBP and they are done making concessions.