I understand your concern, but you have several points where your analysis is, at least in my opinion, a little flawed.
First and foremost being, raids always get easier over time. People have been soloing Rancor in particular for a long while, so a character who is particularly good at doing that specific thing isn't game-breaking in any regard. After all, does it really matter if someone solos with a zVader squad and someone else solos with Luke? They both soloed. They're both in the same drawing for the same rewards. Nerfing toons across the board to suddenly make Rancor harder wouldn't sit well with a lot of players and for good reason. Many of us have been doing that content for a long time. I don't want it to be harder or take more time (that second part being the critical portion). If I'm gonna spend more time in game I want new content.
Secondly, nerfing stats across the board doesn't make mods mean more as you contend, at least not all of them, since ultimately it makes all the percentage based mods mean less. This puts hefty limiters on what's a good mod and what is mostly garbage. This would put even more of a premium on speed secondaries, and that's not a direction I'd like to see the game go.
In the end I'd much rather see the addition of another raid than the type of balance pass you are suggesting. That would allow for more challenging content without pushing us backwards on what we've already spent months doing.
