Hakimi in his first season however played only about two thirds of the matches while Sancho was continuously playing (played all 34 BL matches 18/19). And more importantly he performed regardless of Hakimi playing on the same wing (or at all) as Sancho did (both played on left and right, and not always on the same wing together). This was Sancho's second season, towards the end of his first season he already established himself as a starter.
So you are right if you look at it superficially, Sancho's first full good season was Hakimi's first season in Dortmund. But the correlation between Hakimi's presence and Sancho's performances barely exists.