Obviously the Donna Brazile incident was unacceptable. Still every cable news network was frenemies with Donald. His scandals were a ratings bonanza. His campaign was like a 9 month long car chase people couldn't look away from. That was true well before he won the nomination. Clearly all that free screen time helped him more than it hurt him.
Any help he got after he received the GOP nomination was inadvertent. During the general campaign CNN was to the left of MSNBC with their reporting and commentary.