I disagree with this since another possibility was that it wasn't previously working as intended and got fixed : that's a good enough reason.
There's really no reason at this point to change it, whether it wasn't working as intended or not. First off, people have been farming it for a very long time. Most of the people just getting to it now won't be the highly motivated/dedicated ones, so this will make the hurdle even higher for them, and mostly JUST them.
They obviously removed some file somewhere or changed a value in a spreadsheet, because those droids now lack whatever vulnerability they used to have. I was hitting them 40-50% HARDER than anything else in game. That tells me the vulnerability was intentional. Forgetting about the interrupt for a moment, the loss of vulnerability is the biggest wierdness I can see.
Just freaking fix it by putting it back the way it was already, you don't make a fight harder months after it was introduced. The progression of a game goes in exactly the opposite direction if the people in charge are thinking.