I agree that they are not very common, and honestly I doubt that they will ever be used on anything other than offense against a droid team. I've been working on B2 myself to replace Dathcha on defense to see if that makes a difference on defense (i.e. Nebit (L), Jawa, B2, JE, Scavenger), but there are still probably numerous better defensive lineups out there and I wouldn't expect to see them being used on defense much in even the top 100.
That said, with all of the people building-up anti-droid toons like Jawas, Ugnaught, IGD, etc. for the AAT raid, I would expect that very soon there will be a lot of people with fully-equipped anti-droid squads ready to go. This means if you leave your droids on defense, you should expect to start getting sniped by Jawas in the near-future. I've already been doing it to a certain extent myself in the arena; it's nice to have a guaranteed win.
