Return of Reckoning

I've been playing this for a couple of months now, and I've realised that Scenarios are the best way to exp ... providing you win! However, I have noticed a trend which I cannot seem to work out at, which is the amount of exp you get from the scenarios, and what causes the different amounts. I know ...

I've been playing this for a couple of months now, and I've realised that Scenarios are the best way to exp ... providing you win! However, I have noticed a trend which I cannot seem to work out at, which is the amount of exp you get from the scenarios, and what causes the different amounts. I know ...

As a Choppa I literally cannot do any damage - every attack is blocked/parried and I cannot contribute at all. WTF is going on?

Is this a bug or a mechanic?