I think they need to adjust the threshold for the TMO involvement during general play, limit it to cynical foul play, like a punch to the head or eye gouging. Then when checking for a try, give the TMO slightly more power to check for things like a knock on or foot in touch, but limit it to the number of phases the TMO can go back.
Emphasis needs to be shifted back onto the referees on-field, i would prefer a second on-field referee if it removes the input of the TMO and allows decisions to be checked faster. World Rugby needs to improve their investment in referees as well, they have a $100million product been tarnished by the people officiating the game, if the on-field referees aren't up to the standard then they need to invest in that area, and help them get better.