Grealish is not more of the same (players we already have). Compare him to Sterling, Foden, Bernardo and Kevin.
Unlike Sterling, Grealish is more of a left-sided playmaker than a winger. For instance, Ronaldinho played mostly on the left side, but he wasn't a winger. So, Grealish is nothing like Sterling. His ability to hold on the ball when pressed and create is on a completely different level to Sterling's.
Grealish is better than Foden at keeping possession in the final 3rd and at creating chances. Foden is more direct and poses a bigger goal threat, he is generally more talented, but he is more likely to lose the ball when pressed.
Grealish is more creative than Bernardo, he is more like Kevin in terms of creativity. But he is less direct than Kevin and less likely to lose the ball when pressed. Also, he is better at running at players than both Bernardo and Kevin.
Now, do we really need another playmaker in a team as creative as ours? Well, we barely created anything against Chelsea in the CL final. One of the main reasons was that we couldn't deal with Chelsea's pressing. We couldn't hold on the ball in the final 3rd which diminished our creativity. Arguably, Grealish could give us more stability in the final 3rd in games against teams like Chelsea or Liverpool. More stability in the final 3rd would mean not only more creativity, but also fewer opportunities to get countered. That's why I think that signing Grealish makes a lot of sense, apart from him being a wonderful player. Can't wait to see him next to Foden and KDB.