bramble shield is not an acceptable alternative to the passive ability, both are required, mulch should be dropped. the passive ability gives +14 damage and +360 health per shambler, when maxed. bramble shield gives any ally a damage shield.
Here is the hard info from the LUA files. The total dps with compost is 54.88, per shambler. 52 for minios, 62 for siege and priests. Add it all up and you get 571 dps for all 10 minions total, before items are taken into consideration.
http://spreadsheets.google.com/ccc?key=pmbS09ByNPGE-hT1mq5_XBQ
Know how long it takes those 10 minions to take out an unclean beast? like 6 seconds. extend that to 8 seconds if they got health items. then add your damage in and reduce it back to 6 seconds probably.
The only other thing i'd say about QoT. I think i'm going to have to start dropping 1 point, at least, into the aoe spike thing. Reasoning: it reduces armor (damage can be removed, doesn't matter). All your minions will benefit from armor reduction. UB has high armor, remove most of it and he's taking upwards of 20% more damage.