In my early opinion, ig 100 serves a specific role. He is the droid team defense against other droid teams and aoe. While not sacrificing too much on offense. And also stalling for time while je tries to get his first kill post mortem.
B2 has no clear role on android team, so far as i can tell. By the time the other team buffs, it is too late. Droid team needs a weak hitting debuffer as much as ugnaught. Hk already fills that role (minus a detaunt) and has a great leader skill.
B2 might be situationally good against sunfac plus rg.