This is Messi level. Actually, this might be better than Messi at the same age. Seriously.
Messi played in a dominant Barca team and had much better highlights because other people would take away defenders and score his assists. If Sancho comes to us he will be like that. Messi obviously has demonstrated his worth, Sancho is still mostly potential though he has demonstrated league-best-player form in a top 4 league already. Sancho's awareness, skills and physicality in a less-dominant team seem superior to Messi.
I watched a lot of Dortmund games this season. He is good but a bit wasted in a counter-attacking team (like Messi would be) because while he is fast enough and match-aware enough to be good in the counter-attack, his abilities in a possession team get lost. In a possession team (us post-Bruno), his skills and awareness will be much more valuable.
Actually, he is so good he is wasted as a RW unless he is given full license to roam, a la Messi. He probably also will be a No.10 backup to Bruno but if he is given a chance as a No.10 he will be much, much better than Bruno. This will create major problems for us because he will then want to play there and we will have no RW.
He is so much better than Grealish in that role that we should not even touch Grealish and splurge on a CB and a CDM. We should play Sancho as a backup, and promote Mejbri to get youth options in the Cups and small games.