I suspect that Southgate would probably agree with that. In his presser this morning he wouldn't be drawn on that until he had watched the whole game a couple of times.
I would guess he will think, even if only in hindsight, we needed to get more possession. Whether he will agree that Grealish was the answer to that question or not, I am not sure.
It may also be that the team was just pushed back, or fell deeper believing they could hold on, as teams often do. This may have been counter to Southgates instructions, I don't know.