He is young, no doubt, so was/ is Verstappen though. This can't be considered to be an argument when looking at where he is, that is Formula One, the pinnacle of Motorpsort.
His past results barely hold any significance if one were to objectively look at the competition he faced in F4 and the Toyota Racing Series. Mitch Evans also dominated the Toyota Racing Series at the age of 15, later he could not stand his ground in F2/ GP2.
Most of the drivers Stroll competed against back then have not advanced to any series worth mentioning.
His results in F3 must also be viewed critically either the competition was weak or his had a considerable amount of help from teammates. This seems plausible, because it would explain his deficits, and it is starting to show because Verstappen didn't struggle as much and he jumped from Karting to F1 within two years, and didn't have the advantage of racing in other Formula series when compared to Stroll.
Ocon is another example of a driver that can be compared to Stroll.
He should be racing in Formula Renault or F2, those are the series in which young drivers develop and mature, and prove that they belong in F1.