At Lion Air, the term F/O refers to 'flap operator', not First Officer. The problem is that many of their F/Os are pay-to-fly jocks. Who cares whether they meet the standards expected of an F/O and second in command, as long as they pay their $45000 (or whatever the ridiculous amount is these days).
The real danger is what happens in the event of captain incapacitation? You have a situation whereby the second in command has never flown below 5000ft, nor has he ever conducted an approach in that case, and nor has he ever landed the airplane. Scary or what?