Deathtrap is a situation based skill to use. And while the situation comes up quite often in single player, it does not come up that often in co-op play. My overall suggestion is to use Deathtrap less if you find he is in the way that often. You may feel this lessens the effectiveness of your character, but there again so does having 3 other people there to help you out!
I have not seen any Deathtrap skills change his AI pattern to this point yet, but I have not used the heal-shields ability so that may alter it a bit. He will always pick a target (And most often its the most moronic of them all) and then go up and attack it with a melee or ranged attack depending on if the target is land or air based.
That being said there are pretty much two situations that I will release him in (Again, only in co-op I use him All the time when solo due to using the mechromancer's anarchy build).
- To knock down the annoying flying targets. Deathtrap always has his ranged and melee ranged skills from level 5 onward. Since his ranged attacks always hit he is very handy to take down the drones and such that can fly overhead while you and your team focus on the ground targets.
- Ambush situations. As you mention he is good at gaining agro and this helps in these situations. When you are in a location and open up a chest, complete an objective or whatever that suddenly puts 6+ red dots around you, pop off Deathtrap and he will occupy 1-3 of them depending on how his AI goes.
The overall goal is to use Deathtrap only in situations where you need to control the AI's targeting of yourself and the people you are playing in co-op (or to get rid of an annoying target that is not worth your bullets). Using him in a situation when people are dropping you have to go in with the understanding you are going to be bringing people back up and they are not likely to get second winds.
Hope this helps.
