Kohli was too pig headed to make changes in his game. Except for that last 2018 England tour, he didn't try much to change his game to sort out his weaknesses.Gill has all the shots, its just about temperament. He has backfoot game (which was absent with Kohli). People couldn't see this weakness with Kohli when he was in prime, he was batting so well on the front foot that backfoot was not needed at all... Kohli should have modified his game in the mid-way (during 2016 or so), if so he would have extended his test career a bit more... Now he knows he can't survive in modern tests (no flat pitches anywhere in the world for tests except Pakistan).
Now contrast this with how many times Tendulkar changed his game as per demands of the game.