I think we need changes in siege mechanic.
First pros for raiding:
Make braziers dmg depends on character current BB (when he is not hitting any object), so when you have 100% BB braziers should deal MAX_DMG (10BB/sec right now), but when you drop to 50% BB braziers should deal less dmg maybe 7.5BB/sec and when you get 10% BB dmg should lower even more.
Why?
From my experience running away from braziers fire is part of raid when you may lag and KO easily, so this one should be easier for raiders.
Now pros for defenders:
1. Make braziers MAX_DMG depends on iron purity, but not like food multi x10, it should be some function like sqrt.
Braziers built from high purity iron for example with multi 6.0 should make max dmg sqrt(6) * 10BB/sec = 24.49, should be enough to counter high purity food.
This would also have nice impact of game economy... people would want to get better iron, iron prices would go up as they should, right now 0% purity bar is equal to 30+% (except inpirationals) that is bad for traders and crafters.
2. Make walls health (x2 or x3 always) and soak much higher (x5 only if basher doesn't have right tools):
- simple fence should require axe to get bashed with current soak,
- stone wall - need pick axe to bash with reasonable soak,
- plank fence (I haven't seen lumberjacks with single handed axe cutting large threes. Can we get double handed axes please or make metal axe change dmg when equipped in one hand and larger dmg when using both hands?)
3. Best of all when you have criminal debuff you CAN'T SWAP items on your character... so raiding groups would need to get more numbers to have bashers with proper tools and fighters with swords to protect them (murder should require melee weapon designed to fights like sword)

4. Make structures like houses, owens, smelters etc (other than walls and braziers harder to destroy) by increase BB drain for each hit (increase soak or hp would be nice, but not too much, so people who made mistake could destroy them).