Grealish would be a poor signing as I don't think he has the motivation (assumption from a far)
It at best offers a short term fix assuming a locks in fully but from a human element, it's a tall ask to ask a 30 yo multi millionaire to take a 'step down' and also expect him to put in the hard graft necessary to succeed.
If the price is right, sure but would rather a 22-25 talent on the rise.
We also already have 2 LWs so unless we're looking to play him in the middle it doesn't address any immediate squad concerns