Two important plays outfielders make that never show up in stats are cutting balls off in the gaps and corners and holding runners to first or other bases becasue the ball doesn't go to the fence.
The other is bases saved because they get to the ball and get rid of it quickly or have the kind of arm that holds runners.
The third play is the better than average catch with runners on base. Only a well turned double play can turn a game faster than a running catch in the gap with two outs and the bases full.