I'm not sure we should be that worried about Sano's batting average, as it's a very incomplete stat, doubly so for someone on the extremes of batting profiles like Sano. Obviously, hitting .170 is unacceptable but in today's scoring environment, .250 would be nice but isn't necessary for him to be a well above average hitter.
Right now, his BA is .183 but his OBP is .315... That's an isoD over .130.
If he's walking a lot and climbs back up to the top of the exit velo leaderboard, a .250 batting average would likely turn him into one of the best hitters in the league.
But no matter where his batting average lands on the season, if he keeps his strikeout rate at or close to career lows (~35%) and keeps that exit velo up (climbing the board lately but only after a disastrous start to 2021), he'll be a very good hitter. At that point, the batting average will likely move into an acceptable territory but it's not the stat I'd lead with to evaluate his worth as a hitter. Actually, it's near the bottom of stats I'd look at to evaluate him.