I guess with the leveling system, it could be a more vague guildline for the players to keep in mind while role playing. Levels are close? Try and keep the fight balanced. Enemy much higher level? Players should be able to honestly show themselves being pushed back or hurt. Players much higher than enemy? They can write how the enemy can barely scratch them or toy with them a bit if they want.

Levels of course, shouldn’t be the only factor that decides a fight. Maybe the enemy has a skill that even if they are lower level, makes them tricky or annoying to fight if the players can’t figure out how to counter it. Players can in turn also find ways through the fight to exploit weaknesses or figure a strategy that may tip the scales in their favor in stronger fight. 

The one thing I will say about going this route is that if you can trust your players to role play fairly and not just always somehow have an easy time with everything in the quest because they wrote they did.