What Adam said.
A lot of focus is going on purely combat! Even combat stat wise the knight is twice as good as a thug, so 2 different. It means that a thug has to roll at least 2 better than them. However then you have to take into account the knight having armour three points better, two more wounds, a will rating two better and a shield.
Personally, and it is a bit riskier, I take Barbarians over Knights for the same cost. They are a less armoured but have more wounds and are a lot deadlier in combat when you take a double handed weapon into the equation.
All changing the dice does is stop the knight from getting the overriding victory that they should statistically get more frequently and reduce combat to a slog.
My advice would be to limit the game length as others have suggested - to 5 turns with a 6th happening on a 50/50 roll. Change the rules re treasure tokens so the winner does not take all of the table if they slaughter you outright. What you then see is people having to consider who they will use to get treasure off the table and who will cover their retreat.
Again, in my experience this leads to people using characters much more as you would expect with thieves and thugs becoming baggage lackeys whilst the barbarians etc do the dirty work of cutting down any chasers. Warhounds then become really useful for chasing down any enemy treasure bearers and either slowing them down for you previously mentioned combat skilled characters to catch up with or if lucky, taking them out altogether therefore denying your enemy a treasure.