Comparison to Xavi is irrelevant as it is. Both are part of the trajectory of this team, Xavi got there early in rebuild, basically first to build the current team, Fick is continuing the job and potentially elevating it to a higher level.
But if you really do care to compare and are adamant about it, Flick has to achieve titles. Falling short is on him also. For example, he could have been +6 going into the Clasico if he didn't fuck up the line-up big time vs Osasuna. Errors like that, even 2-3 of those during the season, can endanger a season's hard effort.