I generally try to make all my mods as permanent as possible, to cover as many game modes as possible, for the sole reason of not having to spend any more time than I have to. Considering, and I don't even know how many times I have brought this up, we have Raids, TB, GAC, TW, Conquest, JG, UJ, etc., the last thing I need is to worry about mods. The only times I swap and use layouts is for JG events. So that part doesn't bother me, but I can imagine how frustrating it must be for other players.
As for the second part, about RNG, yeah, 100% agree. It happened to me who knows how many times in the Endor raid, it keeps happening now on Naboo. And for some reason, the current and the last run seemed to be a lot more difficult. I'm slowly improving my score (currently at 4M), but it just seems that recently I've had to restart much more than I used to. For the KB team, I went from G12 to R5, I can understand having to adjust my strategy for that team. But with Maul at R7, for example, I've only been upgrading my mods and getting a bit more speed, I've gotten used to the strategy behind that team, and it's still extremely RNG reliant, especially with that ridiculous bonus turn mechanic.