He has not had time to destroy Netflix because as soon as he announced his purchase Netflix implemented a poison pill change to its corporate governance rules. This was designed to prevent Carl from interfering with the governance of Netflix. Carl might have given Netflix a short stock boost, but Netflix also has been performing well to which he gets zero credit as he does not hold a board seat.
Short term investors like Carl because he can often influence short term changes that are good for some of those short term investors, but he does not care about the long term health of the company. He tried to get Yahoo to sell itself to Microsoft. This nearly destroyed the company. He meddled with Chrysler as well.