are you focussing when shooting w/ Seamus, cuz if you aren't you should be. I have one shoted Zoraida, the Rail Golem, and countless others by doing this.
I like Bag o' Tools, but you have to understand that Seamus isn't a melee master, he is a minion and enforcer killer. I use him as my vp getter/ denial guy, killing his scheme runners, forcing my opponent to change his game to deal with him. The best trigger on the bag is the one that let's him drop a scheme marker in base contact w/the model he damaged. This is perfect for plant explosives, plant evidence, protect territory, breakthrough and so forth. Both upgrades have there place, it just depends on the scheme pool, and your model collection.