Not quite the thing
Definition 1 of 1
Pro Tip 1/3Subtlety
'Not quite the thing' adds a gentle touch to criticism, softening the impact. 
Your essay is well-written but not quite the thing for this competition's theme.
Pro Tip 2/3Expectation Gap
Use when something is close to what was expected but still misses the mark. 
The new policy is not quite the thing we hoped for to address the issues.
Pro Tip 3/3Cultural Fit
It can highlight a mismatch with social or cultural norms or expectations. 
Wearing a casual outfit to the gala was not quite the thing.