career enders would leave a lot of users in a position to quit I think.
True. Career enders should never be even considered.
The thing that bothers most is the total ramdomness involved in injuries.
If we are talking about realism, so some players should be more prone to injuries than others. If a player had a serious injury once, he probably will have more injury concerns in the future. Injuries should be recorded in the player`s history database, and so an injury-prone player should be undervalued in the market. That's much more realistic then the current system.