A 250hr F/O will not necessarily be able to perform perfectly in the real airplane when something unusual is thrown at them even though they will have passed all the tests in the SIM. You need to nurture your inexperienced crew. They are the equivalent of learner drivers.
Presumably the F/O has a command type rating before being qualified to act as second in command of a jet transport. Thank goodness the passengers are not aware the first officer is considered to be the equivalent of a learner driver and needs to be "nurtured.".
Just ask yourself honestly if the situation occurred where the captain becomes incapacitated in the cruise at 37,000 ft would the 250 hour first officer be able to safely fly that aircraft solo IMC all the way from cruise to the landing while making all the radio calls to ATC etc. Especially as his company limits him to a max crosswind component of 15 knots.
The uncomfortable truth is the airlines count on the statistical probability that this combination of circumstances will never happen in our lifetime. Next question please..