the mortars, LeIG, and pack howitzer all have a .25 damage modifier against troops in building. You basically need to use infantry and/or tank to clear out buildings now.
The Centuar have a "regular" .5D/.4A modifier.
update: actually it seems normal tank gun only deal .25 damage to garrisoned infantry as well. You basically need to use infantry in a direct assault.
what is mortar for now???? in coh1, it's garrison counter, and that make sense.
this is soviet mortar description
"barrage weapon. Effective against static infantry and structures"
what is static infantry?
now OKW has no reliable building counter either of T1 and T2 like sniper.