Yes, lowering the injury slider has a massively destabilizing impact on the gameplay....that is why we've been sticking with it this long to assess the long-term viability. Sadly, most people seem to be judging on 1 or 2 games and/or without following the OP exactly.
You can use whatever team you want....I actually would encourage people to try lots of different teams so you can get a feel for different players and player types as well as ratings' impacts. I think you can lose sight on just how well this game plays when using just one team....even if you use 1 for you REAL franchise, having tried other teams can help 1 appreciate the players you do and do not have.